vulkan: add INTEL_XE1 arch enum and enable coopmat1 on Intel Xe-LPG Plus (#24404)

* vulkan: add INTEL_PRE_XE2 arch enum and enable coopmat1 on Intel Xe-LPG Plus (1/3, Xe1-ARLH)

Co-authored-by: Xia, Jie <jie.xia@intel.com>
Co-authored-by: Liu, Russell <russell.liu@intel.com>

* Address comments of bf16 and trailing whitespace

* Rename INTEL_PRE_XE2 to INTEL_XE1 and remove driver workaround

* Add Windows driver check

---------

Co-authored-by: Xia, Jie <jie.xia@intel.com>
Co-authored-by: Liu, Russell <russell.liu@intel.com>

conversion/mamba.py

@@ -114,7 +114,8 @@ class Mamba2Model(TextModel):
             hparams["text_config"] = hparams["llm_config"]
         super().__init__(dir_model, *args, hparams=hparams, **kwargs)
         self.d_model = self.find_hparam(["hidden_size", "d_model", "dim"])
-        self.d_inner = self.find_hparam(["mamba_d_ssm", "intermediate_size", "d_inner"], optional=True) or 2 * self.d_model
+        self.expand = self.find_hparam(["mamba_expand", "expand"], optional=True) or 2
+        self.d_inner = self.find_hparam(["mamba_d_ssm", "intermediate_size", "d_inner"], optional=True) or self.expand * self.d_model
         self.n_group = self.find_hparam(["n_groups"], optional=True) or 1
 
     def set_vocab(self):
@@ -144,11 +145,9 @@ class Mamba2Model(TextModel):
 
         rms_norm_eps = self.find_hparam(["layer_norm_epsilon", "rms_norm_eps"], optional=True) or 1e-5
 
-        # Fail early for models which don't have a block expansion factor of 2
-        # TODO: does this really matter?
         # skip the assertion for FalconH1 Model
         if self.model_arch != gguf.MODEL_ARCH.FALCON_H1:
-            assert self.d_inner == 2 * self.d_model
+            assert self.d_inner == self.expand * self.d_model
             assert self.d_inner % head_dim == 0
 
         self.gguf_writer.add_context_length(2**20)  # arbitrary value; for those who use the default

ggml/src/ggml-cpu/vec.cpp

@@ -75,12 +75,12 @@ void ggml_vec_dot_f32(int n, float * GGML_RESTRICT s, size_t bs, const float * G
             ay1 = GGML_F32_VEC_LOAD(y + i);
             sum1 = GGML_F32_VEC_FMA(sum1, ax1, ay1);
         }
-        // maximum number of leftover elements will be less that ggml_f32_epr. Apply predicated svmad on available elements only
+        // maximum number of leftover elements will be less that ggml_f32_epr. Apply predicated svmla on available elements only
         if (np2 < n) {
             svbool_t pg = svwhilelt_b32(np2, n);
             ax1 = svld1_f32(pg, x + np2);
             ay1 = svld1_f32(pg, y + np2);
-            sum1 = svmad_f32_m(pg, ax1, ay1, sum1);
+            sum1 = svmla_f32_m(pg, sum1, ax1, ay1);
         }
         // reduce sum1,sum2 to sum1
         GGML_F32_VEC_REDUCE(sumf, sum1, sum2, sum3, sum4, sum5, sum6, sum7, sum8);

ggml/src/ggml-cuda/out-prod.cu

@@ -2,6 +2,28 @@
 
 #include <cstdint>
 
+static __global__ void k_compute_out_prod_ptrs(
+        const float * src0_d, const float * src1_d, float * dst_d,
+        const float ** ptrs_a, const float ** ptrs_b, float ** ptrs_c,
+        const int64_t ne2, const int64_t ne3,
+        const int64_t dps2, const int64_t dps3,
+        const size_t s02, const size_t s03,
+        const size_t s12, const size_t s13,
+        const size_t s2,  const size_t s3) {
+    const int64_t i2 = blockIdx.x*blockDim.x + threadIdx.x;
+    const int64_t i3 = blockIdx.y*blockDim.y + threadIdx.y;
+
+    if (i2 >= ne2 || i3 >= ne3) {
+        return;
+    }
+
+    const int64_t idx = i3*ne2 + i2;
+
+    ptrs_a[idx] = src0_d + (i3/dps3)*s03 + (i2/dps2)*s02;
+    ptrs_b[idx] = src1_d +  i3      *s13 +  i2      *s12;
+    ptrs_c[idx] = dst_d  +  i3      *s3  +  i2      *s2;
+}
+
 void ggml_cuda_out_prod(ggml_backend_cuda_context & ctx, ggml_tensor * dst) {
     const ggml_tensor * src0 = dst->src[0];
     const ggml_tensor * src1 = dst->src[1];
@@ -67,18 +89,39 @@ void ggml_cuda_out_prod(ggml_backend_cuda_context & ctx, ggml_tensor * dst) {
                         &beta,  dst_d  +  i3     *s3,  ldc, s2,
                         batch_count));
         }
+    } else if (ne2 > 1 || ne3 > 1) {
+        // dps2 > 1 (src0 broadcast along dim 2 with non-uniform stride) or multiple GEMMs
+        // along dim 3: compute per-GEMM pointers on the device and use a single batched GEMM.
+        GGML_ASSERT(ne3 > 0);
+        GGML_ASSERT(ne2 <= (int64_t) std::numeric_limits<int>::max() / ne3);
+        const int batch_count = (int) (ne2 * ne3);
+
+        ggml_cuda_pool_alloc<const float *> ptrs_a(ctx.pool(), batch_count);
+        ggml_cuda_pool_alloc<const float *> ptrs_b(ctx.pool(), batch_count);
+        ggml_cuda_pool_alloc<      float *> ptrs_c(ctx.pool(), batch_count);
+
+        const dim3 block_dims(16, 16);
+        const dim3 grid_dims((ne2 + block_dims.x - 1)/block_dims.x, (ne3 + block_dims.y - 1)/block_dims.y);
+        k_compute_out_prod_ptrs<<<grid_dims, block_dims, 0, stream>>>(
+            src0_d, src1_d, dst_d,
+            ptrs_a.get(), ptrs_b.get(), ptrs_c.get(),
+            ne2, ne3, dps2, dps3, s02, s03, s12, s13, s2, s3);
+        CUDA_CHECK(cudaGetLastError());
+
+        CUBLAS_CHECK(
+            cublasSgemmBatched(handle, CUBLAS_OP_N, src1_cublas_op,
+                    ne0, ne1, ne01,
+                    &alpha, ptrs_a.get(), lda,
+                            ptrs_b.get(), ldb,
+                    &beta,  ptrs_c.get(), ldc,
+                    batch_count));
     } else {
-        // Fallback: ne2 == 1 (no batching benefit) or dps2 > 1 (src0 broadcast along dim 2
-        // with non-uniform stride; would need cublasSgemmBatched with pointer arrays).
-        for (int64_t i3 = 0; i3 < ne3; ++i3) {
-            for (int64_t i2 = 0; i2 < ne2; ++i2) {
-                CUBLAS_CHECK(
-                    cublasSgemm(handle, CUBLAS_OP_N, src1_cublas_op,
-                            ne0, ne1, ne01,
-                            &alpha, src0_d + (i3/dps3)*s03 + (i2/dps2)*s02, lda,
-                                    src1_d +  i3      *s13 +  i2      *s12, ldb,
-                            &beta,  dst_d  +  i3      *s3  +  i2      *s2,  ldc));
-            }
-        }
+        // ne2 == 1 && ne3 == 1: single GEMM
+        CUBLAS_CHECK(
+            cublasSgemm(handle, CUBLAS_OP_N, src1_cublas_op,
+                    ne0, ne1, ne01,
+                    &alpha, src0_d, lda,
+                            src1_d, ldb,
+                    &beta,  dst_d,  ldc));
     }
 }

ggml/src/ggml-cuda/vendors/hip.h

@@ -48,6 +48,7 @@
 #define cublasSetMathMode(handle, mode) CUBLAS_STATUS_SUCCESS
 #define cublasSetStream hipblasSetStream
 #define cublasSgemm hipblasSgemm
+#define cublasSgemmBatched hipblasSgemmBatched
 #define cublasSgemmStridedBatched hipblasSgemmStridedBatched
 #define cublasStatus_t hipblasStatus_t
 #define cublasOperation_t hipblasOperation_t

ggml/src/ggml-cuda/vendors/musa.h

@@ -32,6 +32,7 @@
 #define cublasSetMathMode mublasSetMathMode
 #define cublasSetStream mublasSetStream
 #define cublasSgemm mublasSgemm
+#define cublasSgemmBatched mublasSgemmBatched
 #define cublasSgemmStridedBatched mublasSgemmStridedBatched
 #define cublasStatus_t mublasStatus_t
 #define cublasOperation_t mublasOperation_t

ggml/src/ggml-sycl/softmax.cpp

@@ -126,7 +126,7 @@ static void soft_max_f32(const float *         x,
             break;
         }
 
-        const float val = sycl::native::exp(vals[col] - max_val);
+        const float val = sycl::native::exp(sycl::max(vals[col] - max_val, -80.0f));
         tmp += val;
         vals[col] = val;
     }
@@ -154,7 +154,7 @@ static void soft_max_f32(const float *         x,
         tmp = warp_reduce_sum<WARP_SIZE>(tmp);
     }
     if (sinks) {
-        tmp += sycl::native::exp(sinks[i02] - max_val);
+        tmp += sycl::native::exp(sycl::max(sinks[i02] - max_val, -80.0f));
     }
     const float inv_sum = 1.0f / tmp;
 

ggml/src/ggml-vulkan/ggml-vulkan.cpp

@@ -308,6 +308,7 @@ enum vk_device_architecture {
     AMD_RDNA1,
     AMD_RDNA2,
     AMD_RDNA3,
+    INTEL_XE1,
     INTEL_XE2,
     NVIDIA_PRE_TURING,
     NVIDIA_TURING,
@@ -365,21 +366,26 @@ static vk_device_architecture get_device_architecture(const vk::PhysicalDevice&
         const std::vector<vk::ExtensionProperties> ext_props = device.enumerateDeviceExtensionProperties();
 
         bool subgroup_size_control = false;
+        bool integer_dot_product = false;
 
         for (const auto& properties : ext_props) {
             if (strcmp("VK_EXT_subgroup_size_control", properties.extensionName) == 0) {
                 subgroup_size_control = true;
+            } else if (strcmp("VK_KHR_shader_integer_dot_product", properties.extensionName) == 0) {
+                integer_dot_product = true;
             }
         }
 
-        if (!subgroup_size_control) {
+        if (!subgroup_size_control || !integer_dot_product) {
             return vk_device_architecture::OTHER;
         }
 
         vk::PhysicalDeviceProperties2 props2;
         vk::PhysicalDeviceSubgroupSizeControlPropertiesEXT subgroup_size_control_props;
+        vk::PhysicalDeviceShaderIntegerDotProductPropertiesKHR integer_dot_props;
 
         props2.pNext = &subgroup_size_control_props;
+        subgroup_size_control_props.pNext = &integer_dot_props;
         device.getProperties2(&props2);
 
         if (subgroup_size_control_props.minSubgroupSize == 16) {
@@ -388,6 +394,9 @@ static vk_device_architecture get_device_architecture(const vk::PhysicalDevice&
             // https://www.intel.com/content/www/us/en/content-details/824434/2024-intel-tech-tour-xe2-and-lunar-lake-s-gpu.html
             // https://www.intel.com/content/www/us/en/docs/oneapi/optimization-guide-gpu/2025-0/intel-xe-gpu-architecture.html
             return vk_device_architecture::INTEL_XE2;
+        } else if (subgroup_size_control_props.minSubgroupSize == 8 &&
+                 integer_dot_product && integer_dot_props.integerDotProduct4x8BitPackedSignedAccelerated) {
+            return vk_device_architecture::INTEL_XE1;
         }
     } else if (props.vendorID == VK_VENDOR_ID_NVIDIA) {
         const std::vector<vk::ExtensionProperties> ext_props = device.enumerateDeviceExtensionProperties();
@@ -3837,7 +3846,7 @@ static void ggml_vk_load_shaders(vk_device& device, vk_pipeline requested) {
             l_warptile = { 256, 128, 128, 16, subgroup_size_8, 64, 2, tm_m, tn_m, tk_m, subgroup_size_8 };
             l_warptile_mmq = l_warptile_mmq_int = { 256, 128, 128, 32, subgroup_size_8, 64, 2, tm_m, tn_m, tk_m, subgroup_size_8 };
             l_warptile_mmq_int_k = { 256, 128, 128, 32, subgroup_size_16, 64, 1, 4, 2, 1, subgroup_size_16 };
-        } else if (device->vendor_id == VK_VENDOR_ID_INTEL && device->coopmat_support && device->architecture == INTEL_XE2) {
+        } else if (device->vendor_id == VK_VENDOR_ID_INTEL && device->coopmat_support) {
             // Xe2/Xe3 with coopmat enabled - warptile performance tuning
             l_warptile = { 512, 128, 128, 16, subgroup_size_8, 32, 2, tm_m, tn_m, tk_m, subgroup_size_8 };
             l_warptile_mmq = { 512, 128, 128, 32, subgroup_size_8, 32, 2, tm_m, tn_m, tk_m, subgroup_size_8 };
@@ -6361,9 +6370,8 @@ static vk_device ggml_vk_get_device(size_t idx) {
                 break;
             case VK_VENDOR_ID_INTEL: {
                 // Current Windows driver does not expose BF16 support.
-                // We only want to use l_warptile if coopmat is available and is Xe2+
-                const bool xe2_with_coopmat = device->coopmat_support && device->architecture == INTEL_XE2;
-                const bool use_l_warptile = (i == GGML_TYPE_BF16) ? (device->coopmat_bf16_support && xe2_with_coopmat) : xe2_with_coopmat;
+                // We only want to use l_warptile if coopmat is available
+                const bool use_l_warptile = (i == GGML_TYPE_BF16) ? (device->coopmat_bf16_support && device->coopmat_support) : device->coopmat_support;
                 device->mul_mat_l[i] = use_l_warptile;
                 device->mul_mat_id_l[i] = use_l_warptile;
                 device->mul_mat_m[i] = true;
@@ -17890,9 +17898,9 @@ static bool ggml_vk_device_is_supported(const vk::PhysicalDevice & vkdev) {
 static bool ggml_vk_khr_cooperative_matrix_support(const vk::PhysicalDeviceProperties& props, const vk::PhysicalDeviceDriverProperties& driver_props, vk_device_architecture arch) {
     switch (props.vendorID) {
     case VK_VENDOR_ID_INTEL:
-        // Only allowing Xe2 GPU at the moment since Xe2 GPU can gain significant performance boost,
-        // while some older hardware (ex. Arc A770) has performance regressions
-        return arch == vk_device_architecture::INTEL_XE2;
+        // Only allowing Xe2/Xe3 GPU and integrated Xe GPUs at the moment since older hardware (ex. Arc A770) has performance regressions.
+        return (arch == vk_device_architecture::INTEL_XE2) ||
+            (arch == vk_device_architecture::INTEL_XE1 && props.deviceType == vk::PhysicalDeviceType::eIntegratedGpu && driver_props.driverID == vk::DriverId::eIntelProprietaryWindows);
     case VK_VENDOR_ID_AMD:
         if (driver_props.driverID == vk::DriverId::eAmdProprietary || driver_props.driverID == vk::DriverId::eAmdOpenSource) {
             // Workaround for AMD proprietary driver reporting support on all GPUs
@@ -17940,6 +17948,8 @@ static uint32_t ggml_vk_intel_shader_core_count(const vk::PhysicalDevice& vkdev)
     case 0xE20B:  // B580
     case 0xE211:  // Pro B60
         return 20;
+    case 0xB080:  // PTL Xe3 LPG 2x6 (12 subslices)
+        return 12;
     default:
         return 0;
     }

ggml/src/ggml-vulkan/vulkan-shaders/conv2d_mm.comp

@@ -158,7 +158,7 @@ const uint32_t Csh_stride = BS_NPQ;
 #ifdef COOPMAT
 const uint32_t Csh_len    = BS_K * Csh_stride;
 #else
-const uint32_t Csh_len    = csh_store != 0 ? BS_K * Csh_stride : 1;
+const uint32_t Csh_len    = csh_store != 0 ? BS_K * Csh_stride : 8; // 8 to workaround compiler bug
 #endif
 shared SHMEM_TYPE Csh[Csh_len];  // K x NPQ
 #endif

ggml/src/ggml-vulkan/vulkan-shaders/conv3d_mm.comp

@@ -144,7 +144,7 @@ const uint32_t Csh_stride = BS_NPQ;
 #ifdef COOPMAT
 const uint32_t Csh_len    = BS_K * Csh_stride;
 #else
-const uint32_t Csh_len    = csh_store != 0 ? BS_K * Csh_stride : 1;
+const uint32_t Csh_len    = csh_store != 0 ? BS_K * Csh_stride : 8; // 8 to workaround compiler bug
 #endif
 shared SHMEM_TYPE Csh[Csh_len];  // K x NPQ
 #endif

src/models/mamba-base.cpp

@@ -169,7 +169,6 @@ ggml_tensor * llm_build_mamba_base::build_mamba2_layer(llm_graph_input_rs * inp,
     GGML_ASSERT(ubatch.equal_seqs());
     GGML_ASSERT(ubatch.n_tokens == n_seq_tokens * n_seqs);
     GGML_ASSERT(d_inner % n_head  == 0);
-    GGML_ASSERT(d_inner % d_state == 0);
     GGML_ASSERT(d_inner % n_group == 0);
 
     ggml_tensor * conv_states_all = mctx_cur->get_r_l(il);

src/models/mamba2.cpp

@@ -39,10 +39,11 @@ void llama_model_mamba2::load_arch_tensors(llama_model_loader &) {
     const int64_t d_inner = hparams.ssm_d_inner;
     const int64_t d_state = hparams.ssm_d_state;
     const int64_t n_group = hparams.ssm_n_group;
-    const int64_t d_in_proj = 2*d_inner + 2*n_group*d_state + n_head;
+    const int64_t dt_rank  = hparams.ssm_dt_rank;
+
+    const int64_t conv_dim = d_inner + 2 * n_group * d_state;
+    const int64_t d_in_proj = d_inner + conv_dim + dt_rank;
 
-    // only an expansion factor of 2 is supported for now
-    GGML_ASSERT(2 * n_embd == d_inner);
 
     tok_embd = create_tensor(tn(LLM_TENSOR_TOKEN_EMBD, "weight"), {n_embd, n_vocab}, 0);
 
@@ -68,11 +69,11 @@ void llama_model_mamba2::load_arch_tensors(llama_model_loader &) {
         layer.ssm_conv1d = create_tensor(tn(LLM_TENSOR_SSM_CONV1D, "weight", i), {d_conv, d_inner + 2*n_group*d_state}, 0);
         layer.ssm_conv1d_b = create_tensor(tn(LLM_TENSOR_SSM_CONV1D, "bias", i), {d_inner + 2*n_group*d_state}, 0);
 
-        layer.ssm_dt_b = create_tensor(tn(LLM_TENSOR_SSM_DT, "bias", i), {n_head}, 0);
+        layer.ssm_dt_b = create_tensor(tn(LLM_TENSOR_SSM_DT, "bias", i), {dt_rank}, 0);
 
         // no "weight" suffix for these
-        layer.ssm_a = create_tensor(tn(LLM_TENSOR_SSM_A, i), {1, n_head}, 0);
-        layer.ssm_d = create_tensor(tn(LLM_TENSOR_SSM_D, i), {1, n_head}, 0);
+        layer.ssm_a = create_tensor(tn(LLM_TENSOR_SSM_A, i), {1, dt_rank}, 0);
+        layer.ssm_d = create_tensor(tn(LLM_TENSOR_SSM_D, i), {1, dt_rank}, 0);
 
         layer.ssm_norm = create_tensor(tn(LLM_TENSOR_SSM_NORM, "weight", i), {d_inner / n_group, n_group}, 0);
 

tests/test-backend-ops.cpp

@@ -7973,6 +7973,9 @@ static std::vector<std::unique_ptr<test_case>> make_test_cases_eval() {
             }
         }
     }
+    for (auto kernel_type : {GGML_TYPE_F32, GGML_TYPE_F16}) {
+        test_cases.emplace_back(new test_conv_2d({ 256, 256, 192, 1 }, { 3, 3, 192, 96 }, kernel_type, 1, 1, 1, 1, 1, 1, false));
+    }
 
     // sycl backend will limit task global_range < MAX_INT
     // test cases for 2D im2col with large input W and H (occurs in stable-diffusion)
@@ -8672,6 +8675,12 @@ static std::vector<std::unique_ptr<test_case>> make_test_cases_eval() {
                                                   256, 16, 16, {ne2, 1}, {1, 1}));
     }
 
+    // nr2 sweep to cover the cublasSgemmBatched pointer-array path (dps2 > 1)
+    for (int64_t nr2 : {8, 16, 32}) {
+        test_cases.emplace_back(new test_out_prod(GGML_TYPE_F32, GGML_TYPE_F32,
+                                                  256, 16, 16, {1, 1}, {nr2, 1}));
+    }
+
     // add_id
     for (ggml_type type_a : {GGML_TYPE_F32}) {
         for (ggml_type type_b : {GGML_TYPE_F32}) {

tests/test-quantize-fns.cpp

@@ -102,21 +102,34 @@ static float dot_product_error(const ggml_type_traits * qfns, const ggml_type_tr
     return fabsf(result - dot_ref) / test_size;
 }
 
-int main(int argc, char * argv[]) {
-    bool verbose = false;
-    const size_t test_size = 32 * 128;
+static int test_vec_dot_f32(bool verbose) {
+    const auto * f32 = ggml_get_type_traits_cpu(GGML_TYPE_F32);
+    int num_failed = 0;
+    for (int n : {1, 2, 3, 5, 7, 8, 15, 16, 17, 31, 33, 63, 67, 127, 129, 193, 255, 1023}) {
+        std::vector<float> a(n);
+        std::vector<float> b(n);
+        generate_data(0.0, n, a.data());
+        generate_data(1.0, n, b.data());
 
-    std::string arg;
-    for (int i = 1; i < argc; i++) {
-        arg = argv[i];
+        float result = 0.0f;
+        f32->vec_dot(n, &result, 0, a.data(), 0, b.data(), 0, 1);
+        const float ref = dot_product(a.data(), b.data(), n);
+        const float error = fabsf(result - ref) / n;
 
-        if (arg == "-v") {
-            verbose = true;
-        } else {
-            fprintf(stderr, "error: unknown argument: %s\n", arg.c_str());
-            return 1;
+        const bool failed = !(error < MAX_QUANTIZATION_REFERENCE_ERROR);
+        num_failed += failed;
+        if (failed || verbose) {
+            printf(" f32 vec_dot n=%4d:                 %s (ref=%f got=%f err=%f)\n",
+                   n, RESULT_STR[failed], ref, result, error);
         }
     }
+    return num_failed;
+}
+
+static int test_vec_dot_q(bool verbose) {
+    int num_failed = 0;
+
+    const size_t test_size = 32 * 128;
 
     std::vector<float> test_data(test_size);
     std::vector<float> test_data2(test_size);
@@ -124,11 +137,6 @@ int main(int argc, char * argv[]) {
     generate_data(0.0, test_data.size(), test_data.data());
     generate_data(1.0, test_data2.size(), test_data2.data());
 
-    ggml_cpu_init();
-
-    int num_failed = 0;
-    bool failed = false;
-
     for (int i = 0; i < GGML_TYPE_COUNT; i++) {
         ggml_type type = (ggml_type) i;
         const auto * qfns = ggml_get_type_traits(type);
@@ -156,7 +164,7 @@ int main(int argc, char * argv[]) {
                 type == GGML_TYPE_IQ3_S   ? MAX_QUANTIZATION_TOTAL_ERROR_3BITS :
                 type == GGML_TYPE_IQ3_XXS ? MAX_QUANTIZATION_TOTAL_ERROR_3BITS_XXS :
                 type == GGML_TYPE_NVFP4   ? MAX_QUANTIZATION_TOTAL_ERROR_FP4 : MAX_QUANTIZATION_TOTAL_ERROR;
-            failed = !(total_error < max_quantization_error);
+            bool failed = !(total_error < max_quantization_error);
             num_failed += failed;
             if (failed || verbose) {
                 printf("%5s absolute quantization error:    %s (%f)\n", ggml_type_name(type), RESULT_STR[failed], total_error);
@@ -171,15 +179,15 @@ int main(int argc, char * argv[]) {
 
             const float vec_dot_error = dot_product_error(qfns, qfns_cpu, test_size, test_data.data(), test_data2.data());
             const float max_allowed_error = type == GGML_TYPE_Q2_K || type == GGML_TYPE_IQ2_XS || type == GGML_TYPE_IQ2_XXS ||
-                                            type == GGML_TYPE_IQ3_XXS || type == GGML_TYPE_IQ3_S || type == GGML_TYPE_IQ2_S
-                                          ? MAX_DOT_PRODUCT_ERROR_LOWBIT
-                                          : type == GGML_TYPE_Q1_0
-                                          ? MAX_DOT_PRODUCT_ERROR_BINARY
-                                          : type == GGML_TYPE_TQ1_0 || type == GGML_TYPE_TQ2_0
-                                          ? MAX_DOT_PRODUCT_ERROR_TERNARY
-                                          : type == GGML_TYPE_NVFP4
-                                          ? MAX_DOT_PRODUCT_ERROR_FP4
-                                          : MAX_DOT_PRODUCT_ERROR;
+                type == GGML_TYPE_IQ3_XXS || type == GGML_TYPE_IQ3_S || type == GGML_TYPE_IQ2_S
+                ? MAX_DOT_PRODUCT_ERROR_LOWBIT
+                : type == GGML_TYPE_Q1_0
+                ? MAX_DOT_PRODUCT_ERROR_BINARY
+                : type == GGML_TYPE_TQ1_0 || type == GGML_TYPE_TQ2_0
+                ? MAX_DOT_PRODUCT_ERROR_TERNARY
+                : type == GGML_TYPE_NVFP4
+                ? MAX_DOT_PRODUCT_ERROR_FP4
+                : MAX_DOT_PRODUCT_ERROR;
             failed = !(vec_dot_error < max_allowed_error);
             num_failed += failed;
             if (failed || verbose) {
@@ -188,6 +196,31 @@ int main(int argc, char * argv[]) {
         }
     }
 
+    return num_failed;
+}
+
+int main(int argc, char * argv[]) {
+    bool verbose = false;
+
+    std::string arg;
+    for (int i = 1; i < argc; i++) {
+        arg = argv[i];
+
+        if (arg == "-v") {
+            verbose = true;
+        } else {
+            fprintf(stderr, "error: unknown argument: %s\n", arg.c_str());
+            return 1;
+        }
+    }
+
+    ggml_cpu_init();
+
+    int num_failed = 0;
+
+    num_failed += test_vec_dot_f32(verbose);
+    num_failed += test_vec_dot_q(verbose);
+
     if (num_failed || verbose) {
         printf("%d tests failed\n", num_failed);
     }

tools/mtmd/clip-model.h

@@ -55,8 +55,7 @@ struct clip_hparams {
     int32_t n_head = 0;
     int32_t n_head_kv = 0;
     int32_t n_layer = 0;
-    // idefics3
-    int32_t n_merge = 0; // number of patch merges **per-side**
+    int32_t n_merge = 1; // number of patch merges **per-side**
 
     // for preprocessor
     int32_t image_longest_edge = 0;
@@ -135,8 +134,7 @@ struct clip_hparams {
     int32_t custom_image_max_tokens = -1;
 
     void set_limit_image_tokens(int n_tokens_min, int n_tokens_max) {
-        const int cur_merge = n_merge == 0 ? 1 : n_merge;
-        const int patch_area = patch_size * patch_size * cur_merge * cur_merge;
+        const int patch_area = patch_size * patch_size * n_merge * n_merge;
         image_min_pixels = (custom_image_min_tokens > 0 ? custom_image_min_tokens : n_tokens_min) * patch_area;
         image_max_pixels = (custom_image_max_tokens > 0 ? custom_image_max_tokens : n_tokens_max) * patch_area;
         warmup_image_size = static_cast<int>(std::sqrt(image_max_pixels));
@@ -145,8 +143,7 @@ struct clip_hparams {
     void set_warmup_n_tokens(int n_tokens) {
         int n_tok_per_side = static_cast<int>(std::sqrt(n_tokens));
         GGML_ASSERT(n_tok_per_side * n_tok_per_side == n_tokens && "n_tokens must be n*n");
-        const int cur_merge = n_merge == 0 ? 1 : n_merge;
-        warmup_image_size = n_tok_per_side * patch_size * cur_merge;
+        warmup_image_size = n_tok_per_side * patch_size * n_merge;
         // TODO: support warmup size for custom token numbers
     }
     // sam vit deepseek-ocr

tools/mtmd/clip.cpp

@@ -1210,6 +1210,9 @@ struct clip_model_loader {
             {
                 std::vector<int> pinpoints;
                 get_arr_int(KEY_IMAGE_GRID_PINPOINTS, pinpoints, false);
+                if (pinpoints.size() % 2 != 0) {
+                    throw std::runtime_error(string_format("%s: image_grid_pinpoints must have an even number of elements, got %zu\n", __func__, pinpoints.size()));
+                }
                 if (!pinpoints.empty()) {
                     for (size_t i = 0; i < pinpoints.size(); i += 2) {
                         hparams.image_res_candidates.push_back({
@@ -1252,15 +1255,16 @@ struct clip_model_loader {
             }
 
             if (is_vision) {
-                int idx_mean = gguf_find_key(ctx_gguf.get(), KEY_IMAGE_MEAN);
-                int idx_std  = gguf_find_key(ctx_gguf.get(), KEY_IMAGE_STD);
-                GGML_ASSERT(idx_mean >= 0 && "image_mean not found");
-                GGML_ASSERT(idx_std >= 0  && "image_std not found");
-                const float * mean_data = (const float *) gguf_get_arr_data(ctx_gguf.get(), idx_mean);
-                const float * std_data  = (const float *) gguf_get_arr_data(ctx_gguf.get(), idx_std);
+                std::vector<float> image_mean;
+                std::vector<float> image_std;
+                get_arr_f32(KEY_IMAGE_MEAN, image_mean, false);
+                get_arr_f32(KEY_IMAGE_STD , image_std, false);
+                if (image_mean.size() < 3 || image_std.size() < 3) {
+                    throw std::runtime_error(string_format("%s: image_mean/image_std arrays must have at least 3 elements, got %zu and %zu\n", __func__, image_mean.size(), image_std.size()));
+                }
                 for (int i = 0; i < 3; ++i) {
-                    hparams.image_mean[i] = mean_data[i];
-                    hparams.image_std[i]  = std_data[i];
+                    hparams.image_mean[i] = image_mean[i];
+                    hparams.image_std[i]  = image_std[i];
                 }
             }
 
@@ -1686,8 +1690,8 @@ struct clip_model_loader {
                 if (hparams.image_size > 65536) {
                     throw std::runtime_error(string_format("%s: image_size (%d) is too large (max 65536)\n", __func__, hparams.image_size));
                 }
-                if (hparams.patch_size <= 0) {
-                    throw std::runtime_error(string_format("%s: patch_size (%d) must be greater than 0\n", __func__, hparams.patch_size));
+                if (hparams.patch_size <= 0 || hparams.patch_size >= 65536) {
+                    throw std::runtime_error(string_format("%s: patch_size (%d) must be positive and less than 65536\n", __func__, hparams.patch_size));
                 }
                 if (hparams.n_embd <= 0) {
                     throw std::runtime_error(string_format("%s: n_embd (%d) must be greater than 0\n", __func__, hparams.n_embd));
@@ -1695,6 +1699,9 @@ struct clip_model_loader {
                 if (hparams.image_max_pixels < hparams.image_min_pixels) {
                     throw std::runtime_error(string_format("%s: image_max_pixels (%d) is less than image_min_pixels (%d)\n", __func__, hparams.image_max_pixels, hparams.image_min_pixels));
                 }
+                if (hparams.n_merge < 0 || hparams.n_merge >= 65536) {
+                    throw std::runtime_error(string_format("%s: n_merge (%d) must be greater than 0 and less than 65536\n", __func__, hparams.n_merge));
+                }
             }
 
             LOG_INF("%s: projector:          %s\n", __func__, proj_type.c_str());
@@ -3067,6 +3074,29 @@ struct clip_model_loader {
         output = gguf_get_val_f32(ctx_gguf.get(), i);
     }
 
+    void get_arr_f32(const std::string & key, std::vector<float> & output, bool required = true) const {
+        const int i = gguf_find_key(ctx_gguf.get(), key.c_str());
+        if (i < 0) {
+            if (required) {
+                throw std::runtime_error("Key not found: " + key);
+            }
+            return;
+        }
+        const auto type = gguf_get_arr_type(ctx_gguf.get(), i);
+        if (type != GGUF_TYPE_FLOAT32) {
+            throw std::runtime_error(string_format("%s: array '%s' has type %d, expected %d (GGUF_TYPE_FLOAT32)\n", __func__, key.c_str(), type, GGUF_TYPE_FLOAT32));
+        }
+        const size_t n = gguf_get_arr_n(ctx_gguf.get(), i);
+        if (n > (size_t) std::numeric_limits<int>::max()) {
+            throw std::runtime_error(string_format("%s: array '%s' is too large (%zu elements)\n", __func__, key.c_str(), n));
+        }
+        output.resize(n);
+        const float * values = (const float *)gguf_get_arr_data(ctx_gguf.get(), i);
+        for (size_t j = 0; j < n; ++j) {
+            output[j] = values[j];
+        }
+    }
+
     void get_string(const std::string & key, std::string & output, bool required = true) const {
         const int i = gguf_find_key(ctx_gguf.get(), key.c_str());
         if (i < 0) {
@@ -3086,11 +3116,18 @@ struct clip_model_loader {
             }
             return;
         }
-        int n = gguf_get_arr_n(ctx_gguf.get(), i);
+        const auto type = gguf_get_arr_type(ctx_gguf.get(), i);
+        if (type != GGUF_TYPE_INT32) {
+            throw std::runtime_error(string_format("%s: array '%s' has type %d, expected %d (GGUF_TYPE_INT32)\n", __func__, key.c_str(), type, GGUF_TYPE_INT32));
+        }
+        const size_t n = gguf_get_arr_n(ctx_gguf.get(), i);
+        if (n > (size_t) std::numeric_limits<int>::max()) {
+            throw std::runtime_error(string_format("%s: array '%s' is too large (%zu elements)\n", __func__, key.c_str(), n));
+        }
         output.resize(n);
         const int32_t * values = (const int32_t *)gguf_get_arr_data(ctx_gguf.get(), i);
-        for (int i = 0; i < n; ++i) {
-            output[i] = values[i];
+        for (size_t j = 0; j < n; ++j) {
+            output[j] = values[j];
         }
     }
 
@@ -3364,8 +3401,8 @@ int clip_n_output_tokens(const clip_ctx * ctx, const clip_image_f32 * img) {
             {
                 // dynamic size
                 int n_merge = ctx->model.hparams.n_merge;
-                int n_patches_x = img->nx() / patch_size / (n_merge > 0 ? n_merge : 1);
-                int n_patches_y = img->ny() / patch_size / (n_merge > 0 ? n_merge : 1);
+                int n_patches_x = img->nx() / patch_size / n_merge;
+                int n_patches_y = img->ny() / patch_size / n_merge;
                 if (ctx->model.token_embd_img_break) {
                     n_patches = n_patches_y * n_patches_x + n_patches_y - 1; // + one [IMG_BREAK] per row, except the last row
                 } else {

tools/mtmd/models/pixtral.cpp

@@ -63,8 +63,8 @@ ggml_cgraph * clip_graph_pixtral::build() {
         // and then concatenate the [IMG_BREAK] token to the end of each row, aka n_patches_per_row dimension
         // after the concatenation, we have a tensor with shape [n_embd, n_patches_per_row + 1, n_rows]
 
-        const int p_y             = n_merge > 0 ? n_patches_y / n_merge : n_patches_y;
-        const int p_x             = n_merge > 0 ? n_patches_x / n_merge : n_patches_x;
+        const int p_y             = n_patches_y / n_merge;
+        const int p_x             = n_patches_x / n_merge;
         const int p_total         = p_x * p_y;
         const int n_embd_text     = cur->ne[0];
         const int n_tokens_output = p_total + p_y - 1; // one [IMG_BREAK] per row, except the last row

tools/mtmd/mtmd-image.cpp

@@ -628,7 +628,7 @@ mtmd_image_preproc_out mtmd_image_preprocessor_llava_uhd::preprocess(const clip_
 mtmd_image_preprocessor_llava_uhd::slice_instructions mtmd_image_preprocessor_llava_uhd::get_slice_instructions(const clip_image_size & original_size) {
     mtmd_image_preprocessor_llava_uhd::slice_instructions res;
     // align slices by patch_size * n_merge so an integer number of merger output tokens fits per slice
-    const int n_merge         = hparams.n_merge > 0 ? hparams.n_merge : 1;
+    const int n_merge         = hparams.n_merge;
     const int patch_size      = hparams.patch_size * n_merge;
     const int slice_size      = hparams.image_size;
     const int original_width  = original_size.width;
@@ -894,7 +894,7 @@ mtmd_image_preproc_out mtmd_image_preprocessor_dyn_size::preprocess(const clip_i
     clip_image_u8 resized_image;
     const clip_image_size original_size = img.get_size();
     // the original pixtral model doesn't have n_merge
-    const int cur_merge = hparams.n_merge == 0 ? 1 : hparams.n_merge;
+    const int cur_merge = hparams.n_merge;
     const clip_image_size target_size = img_tool::calc_size_preserved_ratio(
         original_size,
         hparams.patch_size * cur_merge,

tools/server/CMakeLists.txt

@@ -15,6 +15,8 @@ add_library(${TARGET} STATIC
     server-common.h
     server-context.cpp
     server-context.h
+    server-stream.cpp
+    server-stream.h
     server-tools.cpp
     server-tools.h
     server-schema.cpp

tools/server/README-dev.md

@@ -57,6 +57,7 @@ The core architecture consists of the following components:
 - `server_tokens`: Unified representation of token sequences (supports both text and multimodal tokens); used by `server_task` and `server_slot`.
 - `server_prompt_checkpoint`: For recurrent (e.g., RWKV) and SWA models, stores snapshots of KV cache state. Enables reuse when subsequent requests share the same prompt prefix, saving redundant computation.
 - `server_models`: Standalone component for managing multiple backend instances (used in router mode). It is completely independent of `server_context`.
+- `stream_session_manager`: Process wide owner of resumable SSE stream sessions (`g_stream_sessions`), keyed by conversation id. Backs the replay buffer that lets a client reattach to a generation after an HTTP disconnect. See the "Resumable streaming" section below.
 
 ```mermaid
 graph TD
@@ -117,6 +118,58 @@ Here is an example trace of an API request for text completion:
 - As the response is stateless, `server_res_generator` calls `response->update()` to update the response with the current state.
 - `server_res_generator` then calls `response->to_json()` and passes the response to the HTTP layer.
 
+### Resumable streaming (SSE replay buffer)
+
+By default a streaming generation is bound to its HTTP socket: when the socket drops (refresh, tab close, mobile background, transient network) the generation aborts and the live stream is lost. This feature keeps the generation running server side and lets a client reattach.
+
+It is opt in via the `X-Conversation-Id` header on `POST /v1/chat/completions`. Without the header the OAI strict path is unchanged. The conversation id is the only identity end to end (server map key, client localStorage key, route path), with an optional `::model` suffix for direct routing in router mode.
+
+The feature lives entirely in `server-stream.{h,cpp}` and rests on three types:
+
+- `stream_session`: a bounded ring buffer (4 MiB cap, oldest bytes drop first) plus a condvar. `append` pushes raw SSE bytes, `read_from` drains from any offset and blocks for live bytes or finalize, `finalize` wakes readers, `cancel` stops the producer. One conv maps to at most one live session.
+- `stream_session_manager` (`g_stream_sessions`): owns all sessions keyed by conv id, enforces the one conv one session invariant via `create_or_replace`, and runs a GC thread that drops completed sessions past their TTL.
+- `stream_pipe_producer` / `stream_pipe_consumer`: the write and read ends. The producer owns the session lifetime and finalizes it on destruction; the consumer is read only and never finalizes, so a reader detaching cannot kill a running generation.
+
+Producer side: `server_res_generator` attaches a producer pipe when the header is present. The HTTP content provider mirrors every chunk into the ring before writing it to the socket. While a pipe is attached, `stream_aware_should_stop` ignores peer disconnect, so a dropped socket does not stop generation: only an explicit `DELETE` does. When the peer leaves early, `on_complete` calls `close()`, which drains the rest of the generation into the ring on the http worker.
+
+Lifetime safety: the producer pipe holds a shared `alive` flag also captured by the session cancel hook. `~server_res_generator` calls `cleanup()` to clear that hook while the reader is still alive, so a `cancel` arriving during teardown can never call `stop()` on a freed response. This ordering is the most fragile part of the feature: finalizing or destroying the producer before `cleanup()` runs reintroduces a use after free.
+
+Consumer side: `GET /v1/stream/<conv_id>?from=N` opens a `text/event-stream` that replays buffered bytes from offset `N` and blocks for live bytes, so the browser reattaches like a fresh EventSource. An offset below the dropped prefix returns 400.
+
+Routes:
+
+- `GET /v1/stream/:conv_id?from=N`: replay or live reattach.
+- `POST /v1/streams/lookup` with `{"conversation_ids": [...]}`: returns session status only for ids the caller already owns. There is no listing route, so live sessions cannot be enumerated (an earlier `GET /v1/streams` was removed for exactly this reason).
+- `DELETE /v1/stream/:conv_id`: explicit Stop, idempotent (`evict_and_cancel`).
+
+Router mode binds the same paths to proxy handlers. A `conv_id -> child` map (`conv_models`), populated when a POST is routed, resolves the owning child in one lookup with no polling. The lookup groups ids per child; GET and DELETE proxy straight to the owner. This loopback REST hop is expected to move to a websocket IPC later, swapping only the transport.
+
+Lifecycle: `g_stream_sessions.start_gc()` runs in main after common init, `stop_gc()` runs first in `clean_up()` and finalizes every live session so no reader hangs. Reader blocking and the post drop drain both run on httplib worker threads, which block on a condvar rather than spin.
+
+| Constant | Value | Role |
+| --- | --- | --- |
+| `STREAM_SESSION_TTL_SECONDS` | 300 | retention of a completed session before GC |
+| `STREAM_SESSION_MAX_BYTES` | 4 MiB | ring cap per session |
+| `STREAM_SESSION_GC_INTERVAL_SECONDS` | 60 | GC tick |
+| `STREAM_READ_WAKE_INTERVAL_MS` | 200 | read_from wake to recheck should_stop |
+| `STREAM_LOOKUP_TIMEOUT_MS` | 250 | router to child loopback budget |
+
+```mermaid
+graph TD
+    Client -- "POST + X-Conversation-Id" --> RG[server_res_generator]
+    RG -- attach --> Prod[stream_pipe_producer]
+    Prod -- "write, drain on peer drop" --> Sess
+    subgraph g_stream_sessions
+        Sess[stream_session: ring buffer, 4 MiB]
+        GC[GC thread] -- drop after TTL --> Sess
+    end
+    Sess -- read_from offset --> Cons[stream_pipe_consumer]
+    Cons -- "GET /v1/stream/:id?from=N" --> Client
+    DEL[DELETE /v1/stream/:id] -- evict_and_cancel --> Sess
+```
+
+The diagram shows the buffer touch points. The live wire (chunks streamed to the original client during a normal generation) is the producer's default output, described under "Producer side" above.
+
 ### Testing
 
 `llama-server` includes an automated test suite based on `pytest`.
@@ -223,6 +276,7 @@ The flow for downloading a new model:
 - Speculative decoding: https://github.com/ggml-org/llama.cpp/pull/17808 and rework in https://github.com/ggml-org/llama.cpp/pull/17808
 - INI presets: https://github.com/ggml-org/llama.cpp/pull/17859 (+ refactoring: https://github.com/ggml-org/llama.cpp/pull/18169)
 - Sleeping mode: https://github.com/ggml-org/llama.cpp/pull/18228
+- Resumable streaming (SSE replay buffer): https://github.com/ggml-org/llama.cpp/pull/23226
 
 
 

tools/server/server-context.cpp

@@ -5,6 +5,7 @@
 #include "server-task.h"
 #include "server-queue.h"
 #include "server-schema.h"
+#include "server-stream.h"
 
 #include "build-info.h"
 #include "common.h"
@@ -4022,6 +4023,15 @@ struct server_res_generator : server_http_res {
             queue_tasks.wait_until_no_sleep();
         }
     }
+    ~server_res_generator() override {
+        // cleanup() must run while rd is still alive (rd is destroyed after this body returns)
+        if (spipe) {
+            spipe->cleanup();
+        }
+    }
+    void stop() override {
+        rd.stop();
+    }
     void ok(const json & response_data) {
         status = 200;
         data = safe_json_to_str(response_data);
@@ -4210,8 +4220,10 @@ std::unique_ptr<server_res_generator> server_routes::handle_completions_impl(
                 }
             };
 
+            auto effective_should_stop = stream_aware_should_stop(res_this, req.should_stop);
+
             try {
-                if (req.should_stop()) {
+                if (effective_should_stop()) {
                     SRV_DBG("%s", "stopping streaming due to should_stop condition\n");
                     return false; // should_stop condition met
                 }
@@ -4245,8 +4257,8 @@ std::unique_ptr<server_res_generator> server_routes::handle_completions_impl(
                 // receive subsequent results
                 bool timeout = false;
                 int64_t start_time = ggml_time_ms();
-                auto result = rd.next([&timeout, &req, &start_time, &params]() {
-                    if (req.should_stop()) {
+                auto result = rd.next([&timeout, &start_time, &params, &effective_should_stop]() {
+                    if (effective_should_stop()) {
                         return true; // should_stop condition met
                     } else if (params.sse_ping_interval > 0 && ggml_time_ms() - start_time > (int64_t)params.sse_ping_interval * 1000) {
                         timeout = true;
@@ -4264,7 +4276,7 @@ std::unique_ptr<server_res_generator> server_routes::handle_completions_impl(
 
                 if (result == nullptr) {
                     SRV_DBG("%s", "stopping streaming due to should_stop condition\n");
-                    GGML_ASSERT(req.should_stop());
+                    GGML_ASSERT(effective_should_stop());
                     return false; // should_stop condition met
                 }
 
@@ -4302,6 +4314,10 @@ std::unique_ptr<server_res_generator> server_routes::handle_completions_impl(
         };
     }
 
+    // attach a producer pipe to the response when X-Conversation-Id is present.
+    // the pipe mirrors SSE chunks into the ring buffer and wires up the cancel hook.
+    stream_session_attach_pipe(*res, req.headers);
+
     return res;
 }
 

tools/server/server-http.cpp

@@ -1,5 +1,6 @@
 #include "common.h"
 #include "server-http.h"
+#include "server-stream.h"
 #include "server-common.h"
 #include "ui.h"
 
@@ -456,13 +457,40 @@ static void set_headers(httplib::Response & res, const std::map<std::string, std
     }
 }
 
+// percent-decode a path component (%XX). path params arrive raw from httplib, unlike query
+// params, so a conv id like "conv::model" sent as "conv%3A%3Amodel" must be decoded here to
+// match the value the client put in the X-Conversation-Id header
+static std::string decode_path_component(const std::string & in) {
+    std::string out;
+    out.reserve(in.size());
+    for (size_t i = 0; i < in.size(); i++) {
+        if (in[i] == '%' && i + 2 < in.size()) {
+            auto hex = [](char c) -> int {
+                if (c >= '0' && c <= '9') return c - '0';
+                if (c >= 'a' && c <= 'f') return c - 'a' + 10;
+                if (c >= 'A' && c <= 'F') return c - 'A' + 10;
+                return -1;
+            };
+            int hi = hex(in[i + 1]);
+            int lo = hex(in[i + 2]);
+            if (hi >= 0 && lo >= 0) {
+                out.push_back(char((hi << 4) | lo));
+                i += 2;
+                continue;
+            }
+        }
+        out.push_back(in[i]);
+    }
+    return out;
+}
+
 static std::map<std::string, std::string> get_params(const httplib::Request & req) {
     std::map<std::string, std::string> params;
     for (const auto & [key, value] : req.params) {
         params[key] = value;
     }
     for (const auto & [key, value] : req.path_params) {
-        params[key] = value;
+        params[key] = decode_path_component(value);
     }
     return params;
 }
@@ -497,26 +525,41 @@ static void process_handler_response(server_http_req_ptr && request, server_http
         set_headers(res, response->headers);
         const std::string content_type = response->content_type;
         // convert to shared_ptr as both chunked_content_provider() and on_complete() need to use it
-        std::shared_ptr q_ptr = std::move(request);
-        std::shared_ptr r_ptr = std::move(response);
-        const auto chunked_content_provider = [response = r_ptr](size_t, const httplib::DataSink & sink) -> bool {
+        std::shared_ptr<server_http_req> q_ptr = std::move(request);
+        std::shared_ptr<server_http_res> r_ptr = std::move(response);
+
+        const auto chunked_content_provider = [response = r_ptr](size_t, httplib::DataSink & sink) -> bool {
             std::string chunk;
             const bool has_next = response->next(chunk);
             if (!chunk.empty()) {
+                // mirror into the ring buffer first, the session must reflect every SSE chunk
+                // whether or not the wire write below succeeds
+                if (response->spipe) {
+                    response->spipe->write(chunk.data(), chunk.size());
+                }
                 if (!sink.write(chunk.data(), chunk.size())) {
+                    // peer is gone, stop the wire path here
                     return false;
                 }
                 SRV_DBG("http: streamed chunk: %s\n", chunk.c_str());
             }
             if (!has_next) {
+                // producer reached its natural end on the wire, a later close() skips the drain
+                if (response->spipe) {
+                    response->spipe->done();
+                }
                 sink.done();
                 SRV_DBG("%s", "http: stream ended\n");
             }
             return has_next;
         };
         const auto on_complete = [request = q_ptr, response = r_ptr](bool) mutable {
-            response.reset(); // trigger the destruction of the response object
-            request.reset();  // trigger the destruction of the request object
+            // on a dropped peer, close() drains the rest of the generation into the ring buffer
+            if (response->spipe) {
+                response->spipe->close();
+            }
+            response.reset(); // spipe destructor finalizes the session if attached
+            request.reset();
         };
         res.set_chunked_content_provider(content_type, chunked_content_provider, on_complete);
     } else {

tools/server/server-http.h

@@ -3,6 +3,7 @@
 #include <atomic>
 #include <functional>
 #include <map>
+#include <memory>
 #include <string>
 #include <thread>
 #include <vector>
@@ -10,6 +11,7 @@
 #include <unordered_map>
 
 struct common_params;
+struct stream_pipe_producer; // defined in server-stream.h
 
 // generator-like API for HTTP response generation
 // this object response with one of the 2 modes:
@@ -23,12 +25,20 @@ struct server_http_res {
     std::string data;
     std::map<std::string, std::string> headers;
 
-    // TODO: move this to a virtual function once we have proper polymorphism support
+    // if set, the stream survives a client disconnect: the producer pipe keeps draining into the
+    // ring buffer and finalizes the session on destruction, so no explicit on_stream_end is needed.
+    // shared_ptr (not unique_ptr) so the forward-declared type is safe to delete here.
+    std::shared_ptr<stream_pipe_producer> spipe;
+
     std::function<bool(std::string &)> next = nullptr;
     bool is_stream() const {
         return next != nullptr;
     }
 
+    // called when the session is cancelled (e.g. DELETE /v1/stream/<conv_id>).
+    // server_res_generator overrides this to stop its reader; the default is a no-op.
+    virtual void stop() {}
+
     virtual ~server_http_res() = default;
 };
 

tools/server/server-models.cpp

@@ -1,12 +1,14 @@
 #include "server-common.h"
 #include "server-models.h"
 #include "server-context.h"
+#include "server-stream.h"
 
 #include "build-info.h"
 #include "preset.h"
 #include "download.h"
 
 #include <cpp-httplib/httplib.h> // TODO: remove this once we use HTTP client from download.h
+#include <optional>
 #include <sheredom/subprocess.h>
 
 #include <functional>
@@ -92,6 +94,9 @@ struct server_subproc {
     }
 };
 
+// short loopback budget for the resumable stream router to child JSON calls (probe, lookup,
+// delete). distinct from params.timeout_read/write which only applies to the generation proxy
+static constexpr int STREAM_LOOKUP_TIMEOUT_MS = 250;
 
 static std::filesystem::path get_server_exec_path() {
 #if defined(_WIN32)
@@ -1580,6 +1585,45 @@ static bool is_autoload(const common_params & params, const server_http_req & re
     }
 }
 
+// percent encode one query or path component, covers reserved chars without pulling in
+// httplib::detail. used by the stream routes to forward conversation_id to children safely
+static std::string encode_qs(const std::string & in) {
+    std::string out;
+    out.reserve(in.size() * 3);
+    for (unsigned char c : in) {
+        bool safe = (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9')
+                 || c == '-' || c == '_' || c == '.' || c == '~';
+        if (safe) {
+            out.push_back(char(c));
+        } else {
+            char buf[4];
+            std::snprintf(buf, sizeof(buf), "%%%02X", c);
+            out.append(buf, 3);
+        }
+    }
+    return out;
+}
+
+// resolve the child that owns a conversation's stream session via the conv_id -> model map
+// populated when the POST was routed. single map lookup then a meta lookup, no polling, no
+// parsing of the conv id. returns nullopt when nothing maps, the caller answers not found and
+// the client recovers
+static std::optional<server_model_meta> resolve_child_for_conv(
+        server_models & models, const std::string & conversation_id) {
+    if (conversation_id.empty()) {
+        return std::nullopt;
+    }
+    auto tracked = models.conv_models.lookup(conversation_id);
+    if (!tracked.has_value()) {
+        return std::nullopt;
+    }
+    auto meta = models.get_meta(*tracked);
+    if (meta.has_value() && meta->is_ready()) {
+        return meta;
+    }
+    return std::nullopt;
+}
+
 void server_models_routes::init_routes() {
     this->get_router_props = [this](const server_http_req & req) {
         std::string name = req.get_param("model");
@@ -1628,6 +1672,12 @@ void server_models_routes::init_routes() {
         if (!router_validate_model(name, models, autoload, error_res)) {
             return error_res;
         }
+        // remember which child serves this conversation so the stream routes can route straight
+        // to it without polling, keyed on the exact conv id from the header
+        std::string conv_id = stream_conv_id_from_headers(req.headers);
+        if (!conv_id.empty()) {
+            models.conv_models.remember(conv_id, name);
+        }
         return models.proxy_request(req, method, name, true); // update last usage for POST request only
     };
 
@@ -1819,6 +1869,128 @@ void server_models_routes::init_routes() {
         res_ok(res, {{"success", true}});
         return res;
     };
+
+    this->router_stream_get = [this](const server_http_req & req) {
+        // GET /v1/stream/<conv_id>?from=N. resolve the owning child from the conv_id -> model
+        // map, 404 when nothing maps
+        auto res = std::make_unique<server_http_res>();
+        std::string conv_id = req.get_param("conv_id");
+        if (conv_id.empty()) {
+            res_err(res, format_error_response("Missing conversation id in path", ERROR_TYPE_INVALID_REQUEST));
+            return res;
+        }
+        std::optional<server_model_meta> owner = resolve_child_for_conv(models, conv_id);
+        if (!owner.has_value()) {
+            res_err(res, format_error_response("Stream not found or expired", ERROR_TYPE_NOT_FOUND));
+            return res;
+        }
+        std::string from = req.get_param("from");
+        std::string child_path = "/v1/stream/" + encode_qs(conv_id);
+        if (!from.empty()) {
+            child_path += "?from=" + from;
+        }
+        SRV_INF("proxying stream resume to model %s on port %d, path=%s\n",
+                owner->name.c_str(), owner->port, child_path.c_str());
+        auto proxy = std::make_unique<server_http_proxy>(
+                "GET",
+                "http",
+                CHILD_ADDR,
+                owner->port,
+                child_path,
+                req.headers,
+                req.body,
+                req.files,
+                req.should_stop,
+                params.timeout_read,
+                params.timeout_write);
+        return std::unique_ptr<server_http_res>(std::move(proxy));
+    };
+
+    this->router_streams_lookup = [this](const server_http_req & req) {
+        // POST /v1/streams/lookup. resolve each requested conv id to its owning child via the
+        // map, group the ids per child, and query only the children that actually own some of
+        // them instead of fanning out to every ready child. a child only answers for the ids
+        // it owns, never lists anything else
+        auto res = std::make_unique<server_http_res>();
+        std::vector<std::string> requested;
+        try {
+            json body = json::parse(req.body);
+            if (body.contains("conversation_ids") && body["conversation_ids"].is_array()) {
+                for (const auto & v : body["conversation_ids"]) {
+                    if (v.is_string() && !v.get<std::string>().empty()) {
+                        requested.push_back(v.get<std::string>());
+                    }
+                }
+            }
+        } catch (const std::exception &) {
+            res_ok(res, json::array());
+            return res;
+        }
+
+        // group requested ids by the child port that owns them, drop ids that map to nothing
+        std::unordered_map<int, json> per_child;
+        for (const auto & cid : requested) {
+            auto owner = resolve_child_for_conv(models, cid);
+            if (!owner.has_value()) {
+                continue;
+            }
+            per_child[owner->port].push_back(cid);
+        }
+
+        json aggregated = json::array();
+        for (auto & [port, ids] : per_child) {
+            json child_body = {{"conversation_ids", ids}};
+            httplib::Client cli(CHILD_ADDR, port);
+            cli.set_connection_timeout(0, STREAM_LOOKUP_TIMEOUT_MS * 1000);
+            cli.set_read_timeout(0, STREAM_LOOKUP_TIMEOUT_MS * 1000);
+            cli.set_write_timeout(0, STREAM_LOOKUP_TIMEOUT_MS * 1000);
+            auto resp = cli.Post("/v1/streams/lookup", child_body.dump(), "application/json");
+            if (!resp || resp->status != 200) {
+                continue;
+            }
+            try {
+                json child_arr = json::parse(resp->body);
+                if (!child_arr.is_array()) {
+                    continue;
+                }
+                for (auto & entry : child_arr) {
+                    if (entry.is_object()) {
+                        aggregated.push_back(entry);
+                    }
+                }
+            } catch (const std::exception &) {
+                continue;
+            }
+        }
+        res_ok(res, aggregated);
+        return res;
+    };
+
+    this->router_stream_delete = [this](const server_http_req & req) {
+        // DELETE /v1/stream/<conv_id>. resolve the owning child via the map and forward only to
+        // it, evict_and_cancel is idempotent on the child
+        auto res = std::make_unique<server_http_res>();
+        std::string conv_id = req.get_param("conv_id");
+        if (conv_id.empty()) {
+            res_err(res, format_error_response("Missing conversation id in path", ERROR_TYPE_INVALID_REQUEST));
+            return res;
+        }
+        std::string child_path = "/v1/stream/" + encode_qs(conv_id);
+        auto owner = resolve_child_for_conv(models, conv_id);
+        if (owner.has_value()) {
+            httplib::Client cli(CHILD_ADDR, owner->port);
+            cli.set_connection_timeout(0, STREAM_LOOKUP_TIMEOUT_MS * 1000);
+            cli.set_read_timeout(0, STREAM_LOOKUP_TIMEOUT_MS * 1000);
+            cli.set_write_timeout(0, STREAM_LOOKUP_TIMEOUT_MS * 1000);
+            auto resp = cli.Delete(child_path.c_str());
+            (void) resp; // best effort, 404 and network errors are equivalent to no op
+        }
+        // drop the tracking entry, the session is being torn down
+        models.conv_models.forget(conv_id);
+        res->status = 204;
+        res->content_type = "application/json";
+        return res;
+    };
 }
 
 

tools/server/server-models.h

@@ -11,7 +11,10 @@
 #include <condition_variable>
 #include <functional>
 #include <memory>
+#include <optional>
 #include <set>
+#include <string>
+#include <unordered_map>
 
 /**
  * state diagram:
@@ -126,6 +129,44 @@ private:
     // if true, the next get_meta() will trigger a reload of model list
     bool need_reload = false;
 
+    // conv_id -> model name that currently serves its stream session, lets the resumable stream
+    // routes go straight to the owning child instead of polling every one. populated when
+    // proxy_request forwards a POST carrying an X-Conversation-Id. best effort: a stale entry just
+    // makes the child answer not found and the client recovers. owns its lock, one mutex per struct
+    struct conv_model_tracker {
+        void remember(const std::string & conv_id, const std::string & model) {
+            if (conv_id.empty() || model.empty()) {
+                return;
+            }
+            std::lock_guard<std::mutex> lock(mu);
+            map[conv_id] = model;
+        }
+
+        std::optional<std::string> lookup(const std::string & conv_id) {
+            if (conv_id.empty()) {
+                return std::nullopt;
+            }
+            std::lock_guard<std::mutex> lock(mu);
+            auto it = map.find(conv_id);
+            if (it == map.end()) {
+                return std::nullopt;
+            }
+            return it->second;
+        }
+
+        void forget(const std::string & conv_id) {
+            if (conv_id.empty()) {
+                return;
+            }
+            std::lock_guard<std::mutex> lock(mu);
+            map.erase(conv_id);
+        }
+
+      private:
+        std::mutex                                   mu;
+        std::unordered_map<std::string, std::string> map;
+    };
+
     common_preset_context ctx_preset;
 
     common_params base_params;
@@ -145,6 +186,9 @@ private:
     void notify_sse(const std::string & event, const std::string & model_id, const json & data = nullptr);
 
 public:
+    // conv_id -> model tracker for the resumable stream routes, owns its lock
+    conv_model_tracker conv_models;
+
     server_models(const common_params & params, int argc, char ** argv);
 
     server_response sse; // for real-time updates via SSE endpoint
@@ -268,6 +312,12 @@ struct server_models_routes {
     server_http_context::handler_t get_router_models_sse;
     server_http_context::handler_t post_router_models;
     server_http_context::handler_t del_router_models;
+
+    // router side handlers for the resumable streaming routes. each resolves the child that owns
+    // a conversation through the conv_id -> model map, no probing or fan out
+    server_http_context::handler_t router_stream_get;
+    server_http_context::handler_t router_streams_lookup;
+    server_http_context::handler_t router_stream_delete;
 };
 
 /**

tools/server/server-stream.cpp

@@ -0,0 +1,569 @@
+#include "server-stream.h"
+#include "server-common.h"
+#include "server-http.h"
+#include "server-queue.h"
+
+#include <chrono>
+#include <memory>
+#include <utility>
+
+namespace {
+constexpr int64_t STREAM_SESSION_TTL_SECONDS         = 300;
+constexpr size_t  STREAM_SESSION_MAX_BYTES           = 4 * 1024 * 1024;
+constexpr int64_t STREAM_SESSION_GC_INTERVAL_SECONDS = 60;
+constexpr int64_t STREAM_READ_WAKE_INTERVAL_MS       = 200;
+
+// returns unix time in seconds
+int64_t now_seconds() {
+    return std::chrono::duration_cast<std::chrono::seconds>(
+        std::chrono::system_clock::now().time_since_epoch()
+    ).count();
+}
+}
+
+stream_session::stream_session(std::string conversation_id_, size_t max_bytes_)
+    : conversation_id(std::move(conversation_id_))
+    , started_ts(now_seconds())
+    , prefix_dropped(0)
+    , cap_bytes(max_bytes_)
+    , done(false)
+    , cancelled(false)
+    , completed_ts(0) {
+    buffer.reserve(64 * 1024);
+}
+
+bool stream_session::append(const char * data, size_t len) {
+    if (len == 0) {
+        return true;
+    }
+    {
+        std::lock_guard<std::mutex> lock(mu);
+        if (done.load(std::memory_order_relaxed)) {
+            return false;
+        }
+        if (len >= cap_bytes) {
+            // single chunk bigger than the cap, keep only the tail that fits
+            size_t skip = len - cap_bytes;
+            prefix_dropped += buffer.size() + skip;
+            buffer.clear();
+            buffer.insert(buffer.end(), data + skip, data + len);
+        } else {
+            size_t needed = buffer.size() + len;
+            if (needed > cap_bytes) {
+                size_t to_drop = needed - cap_bytes;
+                buffer.erase(buffer.begin(), buffer.begin() + to_drop);
+                prefix_dropped += to_drop;
+            }
+            buffer.insert(buffer.end(), data, data + len);
+        }
+    }
+    cv.notify_all();
+    return true;
+}
+
+void stream_session::finalize() {
+    bool was_done = done.exchange(true, std::memory_order_acq_rel);
+    if (was_done) {
+        return;
+    }
+    completed_ts.store(now_seconds(), std::memory_order_release);
+    cv.notify_all();
+}
+
+stream_read_status stream_session::read_from(size_t offset,
+        const std::function<bool(const char *, size_t)> & sink,
+        const std::function<bool()> & should_stop) {
+    std::unique_lock<std::mutex> lock(mu);
+    while (true) {
+        if (should_stop && should_stop()) {
+            return stream_read_status::OK;
+        }
+        if (offset < prefix_dropped) {
+            return stream_read_status::OFFSET_LOST;
+        }
+        size_t logical_end = prefix_dropped + buffer.size();
+        if (offset < logical_end) {
+            size_t local_off = offset - prefix_dropped;
+            size_t n         = buffer.size() - local_off;
+            // copy the available chunk under the lock, release before calling the sink
+            std::vector<char> chunk(buffer.begin() + local_off, buffer.begin() + local_off + n);
+            offset += n;
+            lock.unlock();
+            bool keep_going = sink(chunk.data(), chunk.size());
+            if (!keep_going) {
+                return stream_read_status::OK;
+            }
+            lock.lock();
+            continue;
+        }
+        if (done.load(std::memory_order_acquire)) {
+            return stream_read_status::OK;
+        }
+        // wait for new bytes, finalize, or a periodic wake to re check should_stop
+        cv.wait_for(lock, std::chrono::milliseconds(STREAM_READ_WAKE_INTERVAL_MS));
+    }
+}
+
+bool stream_session::is_done() const {
+    return done.load(std::memory_order_acquire);
+}
+
+size_t stream_session::total_size() const {
+    std::lock_guard<std::mutex> lock(mu);
+    return prefix_dropped + buffer.size();
+}
+
+size_t stream_session::dropped_prefix() const {
+    std::lock_guard<std::mutex> lock(mu);
+    return prefix_dropped;
+}
+
+int64_t stream_session::completed_at() const {
+    return completed_ts.load(std::memory_order_acquire);
+}
+
+void stream_session::set_stop_producer(std::function<void()> fn) {
+    std::lock_guard<std::mutex> lock(mu);
+    stop_producer = std::move(fn);
+}
+
+void stream_session::cancel() {
+    // flip cancelled first so the producer-side stream_aware_should_stop can break out of the
+    // recv() wait even if remove_waiting_task_ids does not notify the condvar (the cancel task
+    // posted by rd.stop() will eventually notify, but we do not want to depend on that timing)
+    cancelled.store(true, std::memory_order_release);
+    // copy the hook under the lock then invoke outside, the producer side may grab queue locks
+    // and we do not want to hold our mu across that path
+    std::function<void()> fn;
+    {
+        std::lock_guard<std::mutex> lock(mu);
+        fn = stop_producer;
+    }
+    if (fn) {
+        fn();
+    }
+}
+
+bool stream_session::is_cancelled() const {
+    return cancelled.load(std::memory_order_acquire);
+}
+
+stream_session_manager::stream_session_manager()
+    : running(false) {
+}
+
+stream_session_manager::~stream_session_manager() {
+    stop_gc();
+}
+
+stream_session_ptr stream_session_manager::create_or_replace(const std::string & conversation_id) {
+    // evict any previous session on the same conv, this guarantees the invariant
+    // "one conv = at most one live session" and propagates cancel to its producer
+    stream_session_ptr previous;
+    auto fresh = std::make_shared<stream_session>(conversation_id, STREAM_SESSION_MAX_BYTES);
+    {
+        std::unique_lock<std::shared_mutex> lock(map_mu);
+        auto it = sessions.find(conversation_id);
+        if (it != sessions.end()) {
+            previous = it->second;
+            it->second = fresh;
+        } else {
+            sessions.emplace(conversation_id, fresh);
+        }
+    }
+    if (previous) {
+        previous->cancel();
+        previous->finalize();
+    }
+    return fresh;
+}
+
+stream_session_ptr stream_session_manager::get(const std::string & conversation_id) {
+    std::shared_lock<std::shared_mutex> lock(map_mu);
+    auto it = sessions.find(conversation_id);
+    if (it == sessions.end()) {
+        return nullptr;
+    }
+    return it->second;
+}
+
+std::vector<stream_session_ptr> stream_session_manager::list_all() const {
+    std::vector<stream_session_ptr> out;
+    std::shared_lock<std::shared_mutex> lock(map_mu);
+    out.reserve(sessions.size());
+    for (auto & kv : sessions) {
+        out.push_back(kv.second);
+    }
+    return out;
+}
+
+void stream_session_manager::evict(const std::string & conversation_id) {
+    stream_session_ptr s;
+    {
+        std::unique_lock<std::shared_mutex> lock(map_mu);
+        auto it = sessions.find(conversation_id);
+        if (it == sessions.end()) {
+            return;
+        }
+        s = it->second;
+        sessions.erase(it);
+    }
+    // finalize outside the map lock so any pending readers wake up and exit
+    s->finalize();
+}
+
+void stream_session_manager::evict_and_cancel(const std::string & conversation_id) {
+    stream_session_ptr s;
+    {
+        std::unique_lock<std::shared_mutex> lock(map_mu);
+        auto it = sessions.find(conversation_id);
+        if (it == sessions.end()) {
+            return;
+        }
+        s = it->second;
+        sessions.erase(it);
+    }
+    // signal the producer side first so the inference is cancelled at the queue level,
+    // then finalize, which wakes any pending HTTP reader and lets the drain exit naturally
+    s->cancel();
+    s->finalize();
+}
+
+void stream_session_manager::start_gc() {
+    if (running.exchange(true)) {
+        return;
+    }
+    gc_thread = std::thread([this] { gc_loop(); });
+}
+
+void stream_session_manager::stop_gc() {
+    bool was_running = running.exchange(false);
+    if (was_running) {
+        {
+            std::lock_guard<std::mutex> lock(gc_wake_mu);
+        }
+        gc_wake_cv.notify_all();
+        if (gc_thread.joinable()) {
+            gc_thread.join();
+        }
+    }
+    // finalize all live sessions so no reader ever hangs
+    std::vector<stream_session_ptr> snapshot;
+    {
+        std::unique_lock<std::shared_mutex> lock(map_mu);
+        snapshot.reserve(sessions.size());
+        for (auto & kv : sessions) {
+            snapshot.push_back(kv.second);
+        }
+        sessions.clear();
+    }
+    for (auto & s : snapshot) {
+        s->finalize();
+    }
+}
+
+void stream_session_manager::gc_loop() {
+    while (running.load(std::memory_order_acquire)) {
+        {
+            std::unique_lock<std::mutex> lock(gc_wake_mu);
+            gc_wake_cv.wait_for(lock,
+                std::chrono::seconds(STREAM_SESSION_GC_INTERVAL_SECONDS),
+                [this] { return !running.load(std::memory_order_acquire); });
+        }
+        if (!running.load(std::memory_order_acquire)) {
+            return;
+        }
+        int64_t cutoff = now_seconds() - STREAM_SESSION_TTL_SECONDS;
+        std::vector<stream_session_ptr> to_drop;
+        {
+            std::unique_lock<std::shared_mutex> lock(map_mu);
+            for (auto it = sessions.begin(); it != sessions.end(); ) {
+                int64_t completed = it->second->completed_at();
+                if (completed != 0 && completed <= cutoff) {
+                    to_drop.push_back(it->second);
+                    it = sessions.erase(it);
+                } else {
+                    ++it;
+                }
+            }
+        }
+        // finalize outside the map lock, idempotent if the session was already done
+        for (auto & s : to_drop) {
+            s->finalize();
+        }
+    }
+}
+
+// process wide manager, lifecycle controlled by llama-server main() via start_gc/stop_gc
+stream_session_manager g_stream_sessions;
+
+// stream_pipe ---------------------------------------------------------------------------------
+
+stream_pipe::stream_pipe(stream_session_ptr session)
+    : session_(std::move(session)) {
+}
+
+bool stream_pipe::is_cancelled() const {
+    return session_->is_cancelled();
+}
+
+// stream_pipe_producer
+
+stream_pipe_producer::stream_pipe_producer(stream_session_ptr session)
+    : stream_pipe(std::move(session)) {
+}
+
+stream_pipe_producer::~stream_pipe_producer() {
+    cleanup();
+    session_->finalize();
+}
+
+void stream_pipe_producer::cleanup() {
+    if (!alive_) {
+        return;
+    }
+    alive_->store(false, std::memory_order_release);
+    session_->set_stop_producer(nullptr);
+    alive_.reset();
+}
+
+bool stream_pipe_producer::write(const char * data, size_t len) {
+    return session_->append(data, len);
+}
+
+void stream_pipe_producer::done() {
+    done_ = true;
+}
+
+void stream_pipe_producer::close() {
+    // httplib bails its content provider the moment is_peer_alive() goes false, so pump the rest
+    // of the generation into the ring buffer here. a DELETE flips is_cancelled and cuts it short
+    if (done_ || session_->is_cancelled()) {
+        SRV_INF("stream_pipe close: skip drain (done=%d cancelled=%d) conv=%s\n",
+                done_ ? 1 : 0, session_->is_cancelled() ? 1 : 0, session_->conversation_id.c_str());
+        return;
+    }
+    SRV_INF("stream_pipe close: draining conv=%s\n", session_->conversation_id.c_str());
+    size_t drained = 0;
+    std::string chunk;
+    while (true) {
+        chunk.clear();
+        bool has_next = res_->next(chunk);
+        if (!chunk.empty()) {
+            write(chunk.data(), chunk.size());
+            drained += chunk.size();
+        }
+        if (!has_next) {
+            break;
+        }
+    }
+    SRV_INF("stream_pipe close: drain ended conv=%s bytes=%zu\n", session_->conversation_id.c_str(), drained);
+}
+
+std::shared_ptr<stream_pipe_producer> stream_pipe_producer::create(stream_session_ptr session,
+                                                                   server_http_res & res) {
+    auto alive = std::make_shared<std::atomic<bool>>(true);
+    auto * res_ptr = &res;
+    session->set_stop_producer([alive, res_ptr]() {
+        if (alive->load(std::memory_order_acquire)) {
+            res_ptr->stop();
+        }
+    });
+    auto pipe = std::shared_ptr<stream_pipe_producer>(new stream_pipe_producer(std::move(session)));
+    pipe->alive_ = std::move(alive);
+    pipe->res_   = res_ptr;
+    return pipe;
+}
+
+// stream_pipe_consumer
+
+stream_pipe_consumer::stream_pipe_consumer(stream_session_ptr session)
+    : stream_pipe(std::move(session)) {
+}
+
+stream_read_status stream_pipe_consumer::read(size_t & offset,
+        const std::function<bool(const char *, size_t)> & sink,
+        const std::function<bool()> & should_stop) {
+    return session_->read_from(offset, sink, should_stop);
+}
+
+std::shared_ptr<stream_pipe_consumer> stream_pipe_consumer::create(stream_session_ptr session) {
+    return std::shared_ptr<stream_pipe_consumer>(new stream_pipe_consumer(std::move(session)));
+}
+
+// helper, builds the standard error response and assigns it to a brand new http_res
+static server_http_res_ptr make_error_response(int status, const std::string & message, error_type type) {
+    auto res = std::make_unique<server_http_res>();
+    json err = format_error_response(message, type);
+    res->status = json_value(err, "code", status);
+    res->content_type = "application/json; charset=utf-8";
+    res->data = safe_json_to_str({{"error", err}});
+    return res;
+}
+
+server_http_context::handler_t make_stream_get_handler() {
+    return [](const server_http_req & req) -> server_http_res_ptr {
+        // GET /v1/stream/<conv_id>?from=N replays the SSE bytes already buffered for the
+        // session, blocks for more bytes when the session is still running, returns when
+        // the session is finalized. the body is streamed back as text/event-stream so the
+        // browser EventSource can attach to it like a fresh request
+        std::string conv_id = req.get_param("conv_id");
+        if (conv_id.empty()) {
+            return make_error_response(400, "Missing conversation id in path", ERROR_TYPE_INVALID_REQUEST);
+        }
+        auto session = g_stream_sessions.get(conv_id);
+        if (!session) {
+            return make_error_response(404, "Stream not found or expired", ERROR_TYPE_NOT_FOUND);
+        }
+        size_t from = 0;
+        std::string from_str = req.get_param("from");
+        if (!from_str.empty()) {
+            try {
+                from = static_cast<size_t>(std::stoull(from_str));
+            } catch (const std::exception &) {
+                return make_error_response(400, "Invalid 'from' offset", ERROR_TYPE_INVALID_REQUEST);
+            }
+        }
+        if (from < session->dropped_prefix()) {
+            return make_error_response(400, "Stream offset lost, please restart", ERROR_TYPE_INVALID_REQUEST);
+        }
+        auto res = std::make_unique<server_http_res>();
+        res->status = 200;
+        res->content_type = "text/event-stream";
+        // the next closure reads from the ring buffer at the requested offset, blocks until
+        // bytes arrive or the session finalizes. exit each call after draining the available
+        // chunk so set_chunked_content_provider gets a chance to flush to the socket
+        auto offset_ptr = std::make_shared<size_t>(from);
+        // consumer pipe: read-only, does not finalize the session on destruction
+        auto pipe = stream_pipe_consumer::create(session);
+        res->next = [pipe, offset_ptr, &req](std::string & output) -> bool {
+            bool got_any = false;
+            pipe->read(*offset_ptr,
+                [&](const char * d, size_t n) {
+                    output.append(d, n);
+                    *offset_ptr += n;
+                    got_any = true;
+                    return false;
+                },
+                req.should_stop);
+            return got_any;
+        };
+        return res;
+    };
+}
+
+server_http_context::handler_t make_streams_lookup_handler() {
+    return [](const server_http_req & req) -> server_http_res_ptr {
+        // POST /v1/streams/lookup with body {"conversation_ids": ["X", "Y", ...]} returns the
+        // matching sessions, only for ids the caller already knows. each id matches the exact key
+        // and any "<id>::<model>" variant, so one lookup covers every per model session for a conv
+        std::vector<std::string> requested;
+        try {
+            json body = json::parse(req.body);
+            if (body.contains("conversation_ids") && body["conversation_ids"].is_array()) {
+                for (const auto & v : body["conversation_ids"]) {
+                    if (v.is_string()) {
+                        std::string id = v.get<std::string>();
+                        if (!id.empty()) {
+                            requested.push_back(std::move(id));
+                        }
+                    }
+                }
+            }
+        } catch (const std::exception & e) {
+            auto res = std::make_unique<server_http_res>();
+            res->status = 400;
+            res->content_type = "application/json; charset=utf-8";
+            res->data = safe_json_to_str({{"error", {{"message", std::string("invalid body: ") + e.what()},
+                                                     {"type", "invalid_request_error"}}}});
+            return res;
+        }
+
+        std::vector<stream_session_ptr> sessions;
+        if (!requested.empty()) {
+            auto all = g_stream_sessions.list_all();
+            for (const auto & rid : requested) {
+                const std::string with_sep = rid + "::";
+                for (auto & s : all) {
+                    if (s->conversation_id == rid ||
+                        s->conversation_id.compare(0, with_sep.size(), with_sep) == 0) {
+                        sessions.push_back(s);
+                    }
+                }
+            }
+        }
+
+        json arr = json::array();
+        for (auto & s : sessions) {
+            arr.push_back({
+                {"conversation_id", s->conversation_id},
+                {"is_done",         s->is_done()},
+                {"total_bytes",     s->total_size()},
+                {"started_at",      s->started_ts},
+                {"completed_at",    s->completed_at()},
+            });
+        }
+        auto res = std::make_unique<server_http_res>();
+        res->status = 200;
+        res->content_type = "application/json; charset=utf-8";
+        res->data = safe_json_to_str(arr);
+        return res;
+    };
+}
+
+server_http_context::handler_t make_stream_delete_handler() {
+    return [](const server_http_req & req) -> server_http_res_ptr {
+        // DELETE /v1/stream/<conv_id> is the explicit user Stop, cancels the producer hook
+        // wired by handle_completions_impl and evicts the buffer. idempotent, a session that
+        // already finalized or was never created returns 204 either way
+        std::string conv_id = req.get_param("conv_id");
+        if (conv_id.empty()) {
+            return make_error_response(400, "Missing conversation id in path", ERROR_TYPE_INVALID_REQUEST);
+        }
+        SRV_INF("DELETE /v1/stream/%s -> evict_and_cancel\n", conv_id.c_str());
+        g_stream_sessions.evict_and_cancel(conv_id);
+        auto res = std::make_unique<server_http_res>();
+        res->status = 204;
+        res->content_type = "application/json";
+        return res;
+    };
+}
+
+std::string stream_conv_id_from_headers(const std::map<std::string, std::string> & headers) {
+    // case-insensitive scan for x-conversation-id
+    static constexpr char   target[]   = "x-conversation-id";
+    static constexpr size_t target_len = sizeof(target) - 1;
+    for (const auto & [hk, hv] : headers) {
+        if (hk.size() != target_len) continue;
+        bool match = true;
+        for (size_t i = 0; i < target_len; ++i) {
+            char c = hk[i];
+            if (c >= 'A' && c <= 'Z') c = char(c + 32);
+            if (c != target[i]) { match = false; break; }
+        }
+        if (match) {
+            return hv;
+        }
+    }
+    return std::string();
+}
+
+void stream_session_attach_pipe(server_http_res & res, const std::map<std::string, std::string> & headers) {
+    std::string conversation_id = stream_conv_id_from_headers(headers);
+    SRV_INF("stream_session_attach_pipe: conv_id=%s (empty=%d)\n",
+            conversation_id.c_str(), conversation_id.empty() ? 1 : 0);
+    if (conversation_id.empty()) {
+        return;
+    }
+    auto session = g_stream_sessions.create_or_replace(conversation_id);
+    res.spipe = stream_pipe_producer::create(session, res);
+}
+
+std::function<bool()> stream_aware_should_stop(server_http_res * res, std::function<bool()> fallback) {
+    return [res, fallback = std::move(fallback)]() -> bool {
+        if (res->spipe) {
+            return res->spipe->is_cancelled();
+        }
+        return fallback();
+    };
+}

tools/server/server-stream.h

@@ -0,0 +1,203 @@
+#pragma once
+
+#include "server-http.h"
+
+#include <atomic>
+#include <condition_variable>
+#include <cstddef>
+#include <cstdint>
+#include <functional>
+#include <memory>
+#include <mutex>
+#include <shared_mutex>
+#include <string>
+#include <thread>
+#include <unordered_map>
+#include <vector>
+
+enum class stream_read_status {
+    OK,
+    OFFSET_LOST,
+};
+
+// streaming buffer for one generation, survives HTTP disconnect. the producer appends raw SSE
+// bytes, readers drain from any offset via read_from and block until more bytes or finalize.
+// keyed by conversation_id: one conv = at most one live session
+struct stream_session {
+    std::string conversation_id;
+    int64_t     started_ts; // unix seconds at construction, used by /v1/streams listing
+
+    stream_session(std::string conversation_id_, size_t max_bytes_);
+    stream_session(const stream_session &)             = delete;
+    stream_session & operator=(const stream_session &) = delete;
+
+    // append raw bytes, drops from the front if the cap is reached.
+    // returns false if the session is already finalized
+    bool append(const char * data, size_t len);
+
+    // mark the session as complete, wakes all pending readers
+    void finalize();
+
+    // drain bytes from offset, calling sink for each chunk. blocks until more
+    // bytes arrive or finalize is called. returns OK on clean exit, OFFSET_LOST
+    // if offset falls below the dropped prefix
+    stream_read_status read_from(size_t offset,
+        const std::function<bool(const char *, size_t)> & sink,
+        const std::function<bool()> & should_stop);
+
+    bool    is_done() const;
+    bool    is_cancelled() const;
+    size_t  total_size() const;     // bytes that ever entered the session
+    size_t  dropped_prefix() const; // bytes evicted from the front due to cap
+    int64_t completed_at() const;   // 0 while alive, unix seconds after finalize
+
+    // attach the producer stop hook used to cancel its reader, pass an empty function to detach
+    void set_stop_producer(std::function<void()> fn);
+
+    // signal the producer to abort its inference asap via the stop hook, idempotent
+    void cancel();
+
+private:
+    mutable std::mutex      mu;
+    std::condition_variable cv;
+    std::vector<char>       buffer;
+    size_t                  prefix_dropped;
+    size_t                  cap_bytes;
+    std::atomic<bool>       done;
+    std::atomic<bool>       cancelled;
+    std::atomic<int64_t>    completed_ts;
+    std::function<void()>   stop_producer; // protected by mu
+};
+
+using stream_session_ptr = std::shared_ptr<stream_session>;
+
+// one end of a stream_session pipe. the base holds the session and the shared query, the
+// producer and consumer ends derive from it. virtual dtor so each end runs its own teardown:
+// the producer finalizes the session, the consumer leaves it untouched
+struct stream_pipe {
+    virtual ~stream_pipe() = default;
+
+    // true if the session was cancelled (e.g. via DELETE /v1/stream/<conv_id>)
+    bool is_cancelled() const;
+
+protected:
+    explicit stream_pipe(stream_session_ptr session);
+
+    stream_session_ptr session_;
+};
+
+// producer end: writes chunks into the ring buffer and owns the session lifetime, finalizing it
+// on destruction.
+//
+// lifetime safety: holds a shared_ptr<atomic<bool>> alive also captured by the session's
+// stop_producer hook. cleanup() sets alive=false and clears the hook; it must run while the
+// response the hook calls stop() on is still alive. ~server_res_generator() does this explicitly.
+struct stream_pipe_producer : stream_pipe {
+    ~stream_pipe_producer() override;
+
+    // append raw bytes to the session's ring buffer, returns false if already finalized
+    bool write(const char * data, size_t len);
+
+    // mark the natural end on the wire so a later close() is a no-op
+    void done();
+
+    // on a peer drop, pump the response next() into the ring buffer until done. runs on the http
+    // worker from on_complete, no-op after done() or cancel
+    void close();
+
+    // disarm the stop hook and drop the alive guard, must run while the response the hook
+    // references is still alive. idempotent, the destructor calls it too
+    void cleanup();
+
+    // res.stop() is invoked when the session is cancelled, the alive guard ensures stop() is not
+    // called after cleanup() has run
+    static std::shared_ptr<stream_pipe_producer> create(stream_session_ptr session, server_http_res & res);
+
+private:
+    explicit stream_pipe_producer(stream_session_ptr session);
+
+    bool                                done_ = false;
+    std::shared_ptr<std::atomic<bool>>  alive_;
+    server_http_res *                   res_ = nullptr;
+};
+
+// consumer end: read-only replay of the ring buffer, the destructor does not finalize the session
+struct stream_pipe_consumer : stream_pipe {
+    // drain bytes from offset, calling sink for each available chunk. blocks until more data
+    // arrives or the session finalizes. should_stop is polled, returns OFFSET_LOST if offset
+    // fell below the dropped prefix
+    stream_read_status read(size_t & offset,
+        const std::function<bool(const char *, size_t)> & sink,
+        const std::function<bool()> & should_stop);
+
+    static std::shared_ptr<stream_pipe_consumer> create(stream_session_ptr session);
+
+private:
+    explicit stream_pipe_consumer(stream_session_ptr session);
+};
+
+// owns all live sessions, runs a periodic GC to evict expired ones.
+// the map is keyed by conversation_id, so the invariant "one conv = at most one
+// live session" is enforced at the type level
+class stream_session_manager {
+public:
+    stream_session_manager();
+    ~stream_session_manager();
+
+    stream_session_manager(const stream_session_manager &)             = delete;
+    stream_session_manager & operator=(const stream_session_manager &) = delete;
+
+    // install a new session for this conversation, evicting and cancelling any previous one.
+    // the conversation_id must be non empty, the caller is responsible for that check.
+    // returns the new session
+    stream_session_ptr create_or_replace(const std::string & conversation_id);
+
+    // lookup, returns null if unknown or already evicted
+    stream_session_ptr get(const std::string & conversation_id);
+
+    // list every live or recently completed session, used by GET /v1/streams without filter
+    std::vector<stream_session_ptr> list_all() const;
+
+    // remove from the map and finalize, wakes any pending readers
+    void evict(const std::string & conversation_id);
+
+    // signal the producer to cancel asap then evict, used by the explicit user Stop path
+    void evict_and_cancel(const std::string & conversation_id);
+
+    void start_gc();
+    void stop_gc();
+
+private:
+    void gc_loop();
+
+    mutable std::shared_mutex                           map_mu;
+    std::unordered_map<std::string, stream_session_ptr> sessions; // key: conversation_id
+    std::thread                                         gc_thread;
+    std::atomic<bool>                                   running;
+    std::mutex                                          gc_wake_mu;
+    std::condition_variable                             gc_wake_cv;
+};
+
+// process wide manager, linked by both llama-server and llama-cli. llama-server main() drives
+// start_gc/stop_gc, llama-cli leaves it idle. the dtor calls stop_gc() unconditionally so exit
+// is safe whether or not the GC thread ran
+extern stream_session_manager g_stream_sessions;
+
+// route handler factories operating on g_stream_sessions, wired under /v1/stream/* by server.cpp.
+// keeps the resumable stream surface confined to server-stream
+server_http_context::handler_t make_stream_get_handler();
+server_http_context::handler_t make_streams_lookup_handler();
+server_http_context::handler_t make_stream_delete_handler();
+
+// extract the X-Conversation-Id header value (case-insensitive), empty when absent. exposed so
+// the router can track which child serves a forwarded POST
+std::string stream_conv_id_from_headers(const std::map<std::string, std::string> & headers);
+
+// on an X-Conversation-Id header, create or replace the session and attach a producer pipe to
+// res. no-op when absent, called from the server_res_generator constructor
+void stream_session_attach_pipe(server_http_res & res, const std::map<std::string, std::string> & headers);
+
+// should_stop closure that ignores peer disconnect when a pipe is attached, so only an explicit
+// DELETE stops the producer and generation keeps flowing into the ring buffer. without a pipe it
+// delegates to fallback, the legacy non-resumable flow
+std::function<bool()> stream_aware_should_stop(server_http_res * res, std::function<bool()> fallback);

tools/server/server.cpp

@@ -2,6 +2,7 @@
 #include "server-http.h"
 #include "server-models.h"
 #include "server-cors-proxy.h"
+#include "server-stream.h"
 #include "server-tools.h"
 
 #include "arg.h"
@@ -82,6 +83,10 @@ int llama_server(int argc, char ** argv) {
 
     common_init();
 
+    // start the stream session manager GC right after common init, before any HTTP route can
+    // touch it. lifecycle is symmetric, stop_gc() runs in clean_up() before backend free
+    g_stream_sessions.start_gc();
+
     if (!common_params_parse(argc, argv, params, LLAMA_EXAMPLE_SERVER)) {
         return 1;
     }
@@ -239,6 +244,29 @@ int llama_server(int argc, char ** argv) {
     ctx_http.get ("/slots",                    ex_wrapper(routes.get_slots));
     ctx_http.post("/slots/:id_slot",           ex_wrapper(routes.post_slots));
 
+    // resumable streaming, the conversation_id is the session identity end to end. router and
+    // child wire different handlers under the same paths: a child binds the local g_stream_sessions
+    // backed factories, the router binds proxies that resolve the owning child through the
+    // conv_id -> model map
+    server_http_context::handler_t stream_get_h;
+    server_http_context::handler_t streams_lookup_h;
+    server_http_context::handler_t stream_delete_h;
+    if (is_router_server) {
+        stream_get_h     = models_routes->router_stream_get;
+        streams_lookup_h = models_routes->router_streams_lookup;
+        stream_delete_h  = models_routes->router_stream_delete;
+    } else {
+        stream_get_h     = make_stream_get_handler();
+        streams_lookup_h = make_streams_lookup_handler();
+        stream_delete_h  = make_stream_delete_handler();
+    }
+    ctx_http.get ("/v1/stream/:conv_id",       ex_wrapper(stream_get_h));
+    // POST /v1/streams/lookup with body {"conversation_ids": [...]}. you can only ask for ids
+    // you already own (the WebUI passes the convs visible in its sidebar). the server never
+    // lists ids it has not been asked about, so a random caller cannot enumerate live sessions
+    ctx_http.post("/v1/streams/lookup",        ex_wrapper(streams_lookup_h));
+    ctx_http.del ("/v1/stream/:conv_id",       ex_wrapper(stream_delete_h));
+
     // Google Cloud Platform (Vertex AI) compat
     ctx_http.register_gcp_compat();
 
@@ -314,6 +342,8 @@ int llama_server(int argc, char ** argv) {
 
         clean_up = [&models_routes]() {
             SRV_INF("%s: cleaning up before exit...\n", __func__);
+            // stop the session GC first, it finalizes live sessions and wakes pending readers
+            g_stream_sessions.stop_gc();
             if (models_routes.has_value()) {
                 models_routes->stopping.store(true); // maybe redundant, but just to be safe
                 models_routes->models.unload_all();
@@ -340,6 +370,8 @@ int llama_server(int argc, char ** argv) {
         // setup clean up function, to be called before exit
         clean_up = [&ctx_http, &ctx_server]() {
             SRV_INF("%s: cleaning up before exit...\n", __func__);
+            // stop the session GC first, it finalizes live sessions and wakes pending readers
+            g_stream_sessions.stop_gc();
             ctx_http.stop();
             ctx_server.terminate();
             llama_backend_free();

tools/ui/src/lib/components/app/chat/ChatAttachments/ChatAttachmentsList/ChatAttachmentsListItem/ChatAttachmentsListItemMcpPrompt.svelte

@@ -33,7 +33,7 @@
 
 	{#if !readonly && onRemove}
 		<div
-			class="absolute top-10 right-2 flex items-center justify-center opacity-0 transition-opacity group-hover:opacity-100"
+			class="absolute top-10 right-2 flex items-center justify-center opacity-0 transition-opacity group-focus-within:opacity-100 group-hover:opacity-100"
 		>
 			<ActionIcon icon={X} tooltip="Remove" stopPropagationOnClick onclick={() => onRemove?.()} />
 		</div>

tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageUser/ChatMessageUserPending.svelte

@@ -56,7 +56,7 @@
 			<div class="relative flex h-6 items-center justify-between">
 				<div class="right-0 flex items-center gap-2 opacity-100 transition-opacity">
 					<div
-						class="pointer-events-auto inset-0 flex items-center gap-1 opacity-0 transition-all duration-150 group-hover:opacity-100"
+						class="pointer-events-auto inset-0 flex items-center gap-1 opacity-0 transition-all duration-150 group-focus-within:opacity-100 group-hover:opacity-100"
 					>
 						<ActionIcon icon={Edit} tooltip="Edit" onclick={editCtx.handleEdit} />
 						<ActionIcon icon={Trash2} tooltip="Delete" onclick={onDelete} />

tools/ui/src/lib/components/app/chat/ChatScreen/ChatScreen.svelte

@@ -5,6 +5,7 @@
 		ChatMessages,
 		ChatScreenDragOverlay,
 		ChatScreenProcessingInfo,
+		ChatScreenStreamResumeStatus,
 		ServerLoadingSplash,
 		ChatScreenServerError
 	} from '$lib/components/app';
@@ -281,6 +282,10 @@
 
 			<ChatScreenServerError />
 
+			{#if page.params.id}
+				<ChatScreenStreamResumeStatus />
+			{/if}
+
 			<div class="pointer-events-none flex flex-col gap-6 items-center w-full">
 				{#if (isMobile.current ? mobileScrollDownHint || isMobileUserScrolledUp : autoScroll.userScrolledUp) && page.url.hash.includes(ROUTES.CHAT) && page.params.id}
 					<ChatScreenActionScrollDown

tools/ui/src/lib/components/app/chat/ChatScreen/ChatScreenStreamResumeStatus.svelte

@@ -0,0 +1,18 @@
+<script lang="ts">
+	import { chatStore } from '$lib/stores/chat.svelte';
+	import { StreamConnectionState } from '$lib/enums';
+	import { Loader2 } from '@lucide/svelte';
+
+	let state = $derived(chatStore.streamConnectionState);
+</script>
+
+{#if state === StreamConnectionState.RESUMING}
+	<div
+		class="pointer-events-auto mx-auto mt-2 mb-2 flex max-w-[48rem] items-center gap-2 rounded-md border border-blue-400/40 bg-blue-50/60 px-3 py-1.5 text-sm text-blue-700 dark:bg-blue-950/40 dark:text-blue-200"
+		role="status"
+		aria-live="polite"
+	>
+		<Loader2 class="h-3.5 w-3.5 animate-spin" />
+		<span>Reconnecting to the stream...</span>
+	</div>
+{/if}

tools/ui/src/lib/components/app/chat/index.ts

@@ -683,3 +683,11 @@ export { default as ChatScreenProcessingInfo } from './ChatScreen/ChatScreenProc
  * Rendered inside ChatScreen when `serverError` store has a value.
  */
 export { default as ChatScreenServerError } from './ChatScreen/ChatScreenServerError.svelte';
+
+/**
+ * Stream resume status indicator. Shows a small "Reconnecting to the stream..."
+ * banner with a spinner while `chatStore.streamConnectionState` is `resuming`,
+ * i.e. after a dropped connection is reattaching to the live SSE replay buffer.
+ * Renders nothing otherwise. Shown inside ChatScreen only on an active conversation route.
+ */
+export { default as ChatScreenStreamResumeStatus } from './ChatScreen/ChatScreenStreamResumeStatus.svelte';

tools/ui/src/lib/components/app/navigation/SidebarNavigation/SidebarNavigationConversationItem.svelte

@@ -39,7 +39,6 @@
 		depth = 0
 	}: Props = $props();
 
-	let renderActionsDropdown = $state(false);
 	let dropdownOpen = $state(false);
 
 	let isLoading = $derived(getAllLoadingChats().includes(conversation.id));
@@ -71,26 +70,10 @@
 		}
 	}
 
-	function handleMouseLeave() {
-		if (!dropdownOpen) {
-			renderActionsDropdown = false;
-		}
-	}
-
-	function handleMouseOver() {
-		renderActionsDropdown = true;
-	}
-
 	function handleSelect() {
 		onSelect?.(conversation.id);
 	}
 
-	$effect(() => {
-		if (!dropdownOpen) {
-			renderActionsDropdown = false;
-		}
-	});
-
 	onMount(() => {
 		document.addEventListener('edit-active-conversation', handleGlobalEditEvent as EventListener);
 
@@ -103,23 +86,19 @@
 	});
 </script>
 
-<!-- svelte-ignore a11y_mouse_events_have_key_events -->
-<button
-	class="group flex min-h-9 w-full cursor-pointer items-center justify-between space-x-3 rounded-lg py-1.5 text-left transition-colors hover:bg-foreground/10 {isActive
+<div
+	class="conversation-item group relative flex min-h-9 w-full items-center justify-between space-x-3 rounded-lg py-1.5 transition-colors hover:bg-foreground/10 {isActive
 		? 'bg-foreground/5 text-accent-foreground'
 		: ''} px-3"
-	onclick={handleSelect}
-	onmouseover={handleMouseOver}
-	onmouseleave={handleMouseLeave}
-	onfocusin={handleMouseOver}
-	onfocusout={(e) => {
-		if (!e.currentTarget.contains(e.relatedTarget as Node | null)) {
-			handleMouseLeave();
-		}
-	}}
 >
+	<button
+		class="absolute inset-0 z-0 cursor-pointer rounded-lg focus:outline-none focus-visible:ring-2 focus-visible:ring-ring"
+		onclick={handleSelect}
+		aria-label={conversation.name}
+	>
+	</button>
 	<div
-		class="flex min-w-0 flex-1 items-center gap-2"
+		class="pointer-events-none relative z-10 flex min-w-0 flex-1 items-center gap-2"
 		style:padding-left="{depth * FORK_TREE_DEPTH_PADDING}px"
 	>
 		{#if depth > 0}
@@ -130,7 +109,7 @@
 						<a
 							{...props}
 							href={RouterService.chat(conversation.forkedFromConversationId)}
-							class="flex shrink-0 items-center text-muted-foreground transition-colors hover:text-foreground"
+							class="pointer-events-auto flex shrink-0 items-center text-muted-foreground transition-colors hover:text-foreground"
 						>
 							<GitBranch class="h-3.5 w-3.5" />
 						</a>
@@ -146,18 +125,15 @@
 		{#if isLoading}
 			<Tooltip.Root>
 				<Tooltip.Trigger>
-					<div
-						class="stop-button flex h-4 w-4 shrink-0 cursor-pointer items-center justify-center rounded text-muted-foreground transition-colors hover:text-foreground"
+					<button
+						class="stop-button pointer-events-auto flex h-4 w-4 shrink-0 cursor-pointer items-center justify-center rounded text-muted-foreground transition-colors hover:text-foreground"
 						onclick={handleStop}
-						onkeydown={(e) => e.key === 'Enter' && handleStop(e)}
-						role="button"
-						tabindex="0"
 						aria-label="Stop generation"
 					>
 						<Loader2 class="loading-icon h-3.5 w-3.5 animate-spin" />
 
 						<Square class="stop-icon hidden h-3 w-3 fill-current text-destructive" />
-					</div>
+					</button>
 				</Tooltip.Trigger>
 
 				<Tooltip.Content>
@@ -169,52 +145,50 @@
 		<TruncatedText text={conversation.name} class="text-sm font-medium" showTooltip={false} />
 	</div>
 
-	{#if renderActionsDropdown}
-		<div class="actions flex items-center">
-			<DropdownMenuActions
-				triggerIcon={MoreHorizontal}
-				triggerTooltip="More actions"
-				bind:open={dropdownOpen}
-				actions={[
-					{
-						icon: conversation.pinned ? PinOff : Pin,
-						label: conversation.pinned ? 'Unpin' : 'Pin',
-						onclick: (e: Event) => {
-							e.stopPropagation();
-							handleTogglePin();
-						}
-					},
-					{
-						icon: Pencil,
-						label: 'Edit',
-						onclick: handleEdit,
-						shortcut: ['shift', 'cmd', 'e']
-					},
-					{
-						icon: Download,
-						label: 'Export',
-						onclick: (e: Event) => {
-							e.stopPropagation();
-							conversationsStore.downloadConversation(conversation.id);
-						},
-						shortcut: ['shift', 'cmd', 's']
-					},
-					{
-						icon: Trash2,
-						label: 'Delete',
-						onclick: handleDelete,
-						variant: 'destructive',
-						shortcut: ['shift', 'cmd', 'd'],
-						separator: true
+	<div class="actions pointer-events-auto relative z-20 flex items-center">
+		<DropdownMenuActions
+			triggerIcon={MoreHorizontal}
+			triggerTooltip="More actions"
+			bind:open={dropdownOpen}
+			actions={[
+				{
+					icon: conversation.pinned ? PinOff : Pin,
+					label: conversation.pinned ? 'Unpin' : 'Pin',
+					onclick: (e: Event) => {
+						e.stopPropagation();
+						handleTogglePin();
 					}
-				]}
-			/>
-		</div>
-	{/if}
-</button>
+				},
+				{
+					icon: Pencil,
+					label: 'Edit',
+					onclick: handleEdit,
+					shortcut: ['shift', 'cmd', 'e']
+				},
+				{
+					icon: Download,
+					label: 'Export',
+					onclick: (e: Event) => {
+						e.stopPropagation();
+						conversationsStore.downloadConversation(conversation.id);
+					},
+					shortcut: ['shift', 'cmd', 's']
+				},
+				{
+					icon: Trash2,
+					label: 'Delete',
+					onclick: handleDelete,
+					variant: 'destructive',
+					shortcut: ['shift', 'cmd', 'd'],
+					separator: true
+				}
+			]}
+		/>
+	</div>
+</div>
 
 <style>
-	button {
+	.conversation-item {
 		:global([data-slot='dropdown-menu-trigger']:not([data-state='open'])) {
 			opacity: 0;
 		}
@@ -239,7 +213,8 @@
 			}
 		}
 
-		&:is(:hover) .stop-button {
+		&:is(:hover) .stop-button,
+		&:focus-within .stop-button {
 			:global(.stop-icon) {
 				display: block;
 			}

tools/ui/src/lib/constants/api-endpoints.ts

@@ -21,5 +21,11 @@ export const API_TOOLS = {
 	EXECUTE: '/tools'
 };
 
+// resumable stream routes, the conv::model identity is appended as a path segment
+export const API_STREAM = {
+	BASE: './v1/stream',
+	LOOKUP: './v1/streams/lookup'
+};
+
 /** CORS proxy endpoint path */
 export const CORS_PROXY_ENDPOINT = '/cors-proxy';

tools/ui/src/lib/constants/index.ts

@@ -46,6 +46,7 @@ export * from './routes';
 export * from './sandbox';
 export * from './settings-keys';
 export * from './settings-registry';
+export * from './stream';
 export * from './supported-file-types';
 export * from './table-html-restorer';
 export * from './title-generation';

tools/ui/src/lib/constants/storage.ts

@@ -26,6 +26,9 @@ export const THINKING_ENABLED_DEFAULT_LOCALSTORAGE_KEY = `${STORAGE_APP_NAME}.th
 export const REASONING_EFFORT_DEFAULT_LOCALSTORAGE_KEY = `${STORAGE_APP_NAME}.reasoningEffortDefault`;
 export const USER_OVERRIDES_LOCALSTORAGE_KEY = `${STORAGE_APP_NAME}.userOverrides`;
 
+/** Key prefix for per-conversation resumable stream state, conversationId is appended */
+export const STREAM_RESUME_LOCALSTORAGE_KEY_PREFIX = `${STORAGE_APP_NAME}.streamResume.`;
+
 // Deprecated old key names (kept for backward compat while users migrate)
 /** @deprecated Use {@link ALWAYS_ALLOWED_TOOLS_LOCALSTORAGE_KEY} instead */
 export const DEPRECATED_ALWAYS_ALLOWED_TOOLS_LOCALSTORAGE_KEY = `${STORAGE_APP_NAME_DEPRECATED}.alwaysAllowedTools`;

tools/ui/src/lib/constants/stream.ts

@@ -0,0 +1,3 @@
+// grace window after a visibilitychange before we kick a reader whose socket likely died
+// while the tab was hidden. covers brief background pauses without thrashing live streams
+export const STREAM_VISIBILITY_KICK_MS = 1000;

tools/ui/src/lib/enums/chat.enums.ts

@@ -5,6 +5,15 @@ export enum ChatMessageStatsView {
 	SUMMARY = 'summary'
 }
 
+/**
+ * Connection state of a streamed completion, drives the resume status indicator.
+ */
+export enum StreamConnectionState {
+	STREAMING = 'streaming',
+	RESUMING = 'resuming',
+	LOST = 'lost'
+}
+
 /**
  * Reasoning format options for API requests.
  */

tools/ui/src/lib/enums/index.ts

@@ -10,6 +10,7 @@ export { AgenticSectionType, ContinueIntentKind, ToolCallType } from './agentic.
 
 export {
 	ChatMessageStatsView,
+	StreamConnectionState,
 	ContentPartType,
 	ConversationSelectionMode,
 	ErrorDialogType,

tools/ui/src/lib/services/chat.service.ts

@@ -1,6 +1,7 @@
-import { getJsonHeaders } from '$lib/utils/api-headers';
+import { getAuthHeaders, getJsonHeaders } from '$lib/utils/api-headers';
 import { formatAttachmentText } from '$lib/utils/formatters';
 import { isAbortError } from '$lib/utils/abort';
+import { streamIdentity } from '$lib/utils/stream-identity';
 import {
 	ATTACHMENT_LABEL_PDF_FILE,
 	ATTACHMENT_LABEL_MCP_PROMPT,
@@ -13,7 +14,10 @@ import {
 	CONTROL_ACTION,
 	SSE_LINE_SEPARATOR,
 	SSE_DATA_PREFIX,
-	SSE_DONE_MARKER
+	SSE_DONE_MARKER,
+	STREAM_VISIBILITY_KICK_MS,
+	STREAM_RESUME_LOCALSTORAGE_KEY_PREFIX,
+	API_STREAM
 } from '$lib/constants';
 import {
 	AttachmentType,
@@ -21,12 +25,14 @@ import {
 	FileTypeAudio,
 	MessageRole,
 	MimeTypeAudio,
-	ReasoningFormat
+	ReasoningFormat,
+	StreamConnectionState
 } from '$lib/enums';
 import type {
 	ApiChatMessageContentPart,
 	ApiChatMessageData,
-	ApiChatCompletionToolCall
+	ApiChatCompletionToolCall,
+	ApiStreamSession
 } from '$lib/types/api';
 import type {
 	AudioInputFormat,
@@ -54,6 +60,19 @@ function getAudioInputFormat(mimeType: string): AudioInputFormat {
 	return FileTypeAudio.MP3;
 }
 
+interface ResumableStreamState {
+	bytesReceived: number;
+	updatedAt: number;
+
+	// model frozen at POST time, lets a reload rebuild the exact conv::model identity the
+	// server keyed the session under. null when the POST carried no explicit model
+	model?: string | null;
+}
+
+function streamStorageKey(conversationId: string): string {
+	return STREAM_RESUME_LOCALSTORAGE_KEY_PREFIX + conversationId;
+}
+
 export class ChatService {
 	/**
 	 *
@@ -128,6 +147,7 @@ export class ChatService {
 			onChunk,
 			onComplete,
 			onError,
+			onConnectionState,
 			onReasoningChunk,
 			onToolCallChunk,
 			onModel,
@@ -312,9 +332,16 @@ export class ChatService {
 		}
 
 		try {
+			const headers: Record<string, string> = { ...getJsonHeaders() };
+			// tag streaming requests with the conversation id, this single header is the opt in for the
+			// server side replay buffer and powers discoverActiveStream on tab reopen. with an explicit
+			// model the ::model suffix keeps the per model session distinct
+			if (stream && conversationId) {
+				headers['X-Conversation-Id'] = streamIdentity(conversationId, options.model);
+			}
 			const response = await fetch(API_CHAT.COMPLETIONS, {
 				method: 'POST',
-				headers: getJsonHeaders(),
+				headers,
 				body: JSON.stringify(requestBody),
 				signal
 			});
@@ -341,7 +368,9 @@ export class ChatService {
 					onCompletionId,
 					onTimings,
 					conversationId,
-					signal
+					signal,
+					onConnectionState,
+					options.model
 				);
 
 				return;
@@ -473,6 +502,116 @@ export class ChatService {
 	 * @param excludeReasoning - Whether to strip reasoning content (should match excludeReasoningFromContext setting)
 	 * @param signal - Optional AbortSignal to cancel the pre-encode request
 	 */
+	static async cancelServerStream(conversationId: string, model?: string | null): Promise<void> {
+		if (!conversationId) return;
+		try {
+			const id = streamIdentity(conversationId, model);
+			await fetch(`${API_STREAM.BASE}/${encodeURIComponent(id)}`, {
+				method: 'DELETE',
+				headers: getAuthHeaders()
+			});
+		} catch (e) {
+			console.warn('cancelServerStream failed:', e);
+		}
+	}
+
+	/**
+	 * Pick the running session to splice into when discoverActiveStream lists candidates for a
+	 * conversation. Finalized sessions are not candidates: their final content was already written
+	 * to the DB by the original onComplete handler, so attaching to them would replay a buffer that
+	 * may not match what the DB holds. A continue session's buffer holds only the appended deltas,
+	 * not the pre continue prefix, so replaying it as a fresh generation would erase the original.
+	 *
+	 * Among running sessions we tie break on the most recent started_at, which covers the case of
+	 * multiple inferences left running on the same conversation.
+	 */
+	static selectActiveStream(
+		sessions: ApiStreamSession[] | null | undefined
+	): ApiStreamSession | null {
+		if (!Array.isArray(sessions) || sessions.length === 0) {
+			return null;
+		}
+		const running = sessions.filter((s) => !s.is_done);
+		if (running.length === 0) {
+			return null;
+		}
+		return running.reduce((best, cur) => (cur.started_at > best.started_at ? cur : best));
+	}
+
+	// persist the running byte count and the frozen model for a conversation, a later visit
+	// resumes the SSE replay at the right offset under the same conv::model identity
+	static saveStreamState(
+		conversationId: string,
+		bytesReceived: number,
+		model?: string | null
+	): void {
+		if (!conversationId) return;
+		try {
+			const state: ResumableStreamState = {
+				bytesReceived,
+				updatedAt: Date.now(),
+				model: model ?? null
+			};
+			localStorage.setItem(streamStorageKey(conversationId), JSON.stringify(state));
+		} catch {
+			// localStorage may be full or disabled, silently ignore
+		}
+	}
+
+	static getStreamState(conversationId: string): ResumableStreamState | null {
+		if (!conversationId) return null;
+		try {
+			const raw = localStorage.getItem(streamStorageKey(conversationId));
+			if (!raw) return null;
+			const parsed = JSON.parse(raw) as ResumableStreamState;
+			if (!parsed || typeof parsed.bytesReceived !== 'number') return null;
+			return parsed;
+		} catch {
+			return null;
+		}
+	}
+
+	static clearStreamState(conversationId: string): void {
+		if (!conversationId) return;
+		try {
+			localStorage.removeItem(streamStorageKey(conversationId));
+		} catch {
+			// nothing to do
+		}
+	}
+
+	/**
+	 * Rebuild the stream identity for a resume. The model persisted at POST time wins, including a
+	 * stored null which means the POST carried no explicit model so the identity stays the bare conv
+	 * id. Only fall back to the caller supplied current model when nothing was persisted.
+	 */
+	static resumeStreamIdentity(
+		conversationId: string,
+		state: ResumableStreamState | null,
+		fallbackModel: string | null
+	): string {
+		const model = state && state.model !== undefined ? state.model : fallbackModel;
+		return streamIdentity(conversationId, model);
+	}
+
+	/**
+	 * Reconnect to an interrupted stream for this conversation. Returns the fetch Response so the
+	 * existing SSE parser drains it like a fresh stream. The server returns 200 on success, 404 if
+	 * no session exists for the conv_id, and 400 if the offset is below the dropped prefix.
+	 */
+	static async resumeStream(
+		conversationId: string,
+		signal?: AbortSignal,
+		model?: string | null
+	): Promise<Response | null> {
+		if (!conversationId) return null;
+		const state = ChatService.getStreamState(conversationId);
+		const from = state?.bytesReceived ?? 0;
+		const id = streamIdentity(conversationId, model);
+		const url = `${API_STREAM.BASE}/${encodeURIComponent(id)}?from=${from}`;
+		return await fetch(url, { method: 'GET', signal, headers: getAuthHeaders() });
+	}
+
 	static async preEncode(
 		messages: ApiChatMessageData[] | (DatabaseMessage & { extra?: DatabaseMessageExtra[] })[],
 		model?: string | null,
@@ -557,7 +696,7 @@ export class ChatService {
 	 * @returns {Promise<void>} Promise that resolves when streaming is complete
 	 * @throws {Error} if the stream cannot be read or parsed
 	 */
-	private static async handleStreamResponse(
+	static async handleStreamResponse(
 		response: Response,
 		onChunk?: (chunk: string) => void,
 		onComplete?: (
@@ -573,15 +712,34 @@ export class ChatService {
 		onCompletionId?: (id: string) => void,
 		onTimings?: (timings?: ChatMessageTimings, promptProgress?: ChatMessagePromptProgress) => void,
 		conversationId?: string,
-		abortSignal?: AbortSignal
+		abortSignal?: AbortSignal,
+		onConnectionState?: (state: StreamConnectionState) => void,
+		streamModel?: string | null
 	): Promise<void> {
-		const reader = response.body?.getReader();
+		let reader = response.body?.getReader();
 
 		if (!reader) {
 			throw new Error('No response body');
 		}
 
-		const decoder = new TextDecoder();
+		// bytesParsed is the absolute server side buffer offset of the next byte to parse
+		// segmentStartOffset is the absolute offset where the current reader started, reset on resume
+		// segmentBytesRead is wire bytes read by the current reader
+		let bytesParsed = 0;
+		let segmentStartOffset = 0;
+		let segmentBytesRead = 0;
+		let lastByteAt = Date.now();
+		// each resume must produce at least one byte to be retried again
+		// if a resume returns 200 but yields nothing, we abandon
+		// since the session has a bounded size, the total number of retries is bounded by construction
+		let madeProgress = true;
+		const encoder = new TextEncoder();
+		if (conversationId) {
+			ChatService.saveStreamState(conversationId, 0, streamModel);
+		}
+		onConnectionState?.(StreamConnectionState.STREAMING);
+
+		let decoder = new TextDecoder();
 		let aggregatedContent = '';
 		let fullReasoningContent = '';
 		let aggregatedToolCalls: ApiChatCompletionToolCall[] = [];
@@ -633,84 +791,180 @@ export class ChatService {
 			}
 		};
 
+		const onVisibilityChange = () => {
+			if (typeof document === 'undefined') return;
+			if (document.visibilityState !== 'visible') return;
+			if (streamFinished) return;
+			if (!conversationId) return;
+			// the bytes have been quiet for too long, the OS likely killed the socket
+			// kicking the reader unblocks reader.read with done=true so the outer loop can resume
+			if (Date.now() - lastByteAt > STREAM_VISIBILITY_KICK_MS) {
+				reader!.cancel().catch(() => {});
+			}
+		};
+		if (typeof document !== 'undefined') {
+			document.addEventListener('visibilitychange', onVisibilityChange);
+		}
+
 		try {
 			let chunk = '';
+			// outer loop drives the resume cycle, swaps reader on premature end of stream
 			while (true) {
-				if (abortSignal?.aborted) break;
-
-				const { done, value } = await reader.read();
-				if (done) break;
-
-				if (abortSignal?.aborted) break;
-
-				chunk += decoder.decode(value, { stream: true });
-				const lines = chunk.split(SSE_LINE_SEPARATOR);
-				chunk = lines.pop() || '';
-
-				for (const line of lines) {
+				while (true) {
 					if (abortSignal?.aborted) break;
 
-					if (line.startsWith(SSE_DATA_PREFIX)) {
-						const data = line.slice(SSE_DATA_PREFIX.length).trim();
-						if (data === SSE_DONE_MARKER) {
-							streamFinished = true;
-
-							continue;
+					let done: boolean;
+					let value: Uint8Array | undefined;
+					try {
+						const r = await reader.read();
+						done = r.done;
+						value = r.value;
+					} catch (readErr) {
+						// reader.read() rejects with TypeError when the underlying connection drops
+						// instead of just resolving with done=true. treat it like done so the outer
+						// loop swaps reader via the resume path
+						if (isAbortError(readErr)) {
+							throw readErr;
 						}
+						console.warn('reader.read() rejected, treating as premature end:', readErr);
+						done = true;
+						value = undefined;
+					}
+					if (done) break;
 
-						try {
-							const parsed: ApiChatCompletionStreamChunk = JSON.parse(data);
-							const choice = parsed.choices?.[0];
-							const content = choice?.delta?.content;
-							const reasoningContent = choice?.delta?.reasoning_content;
-							const toolCalls = choice?.delta?.tool_calls;
-							const timings = parsed.timings;
-							const promptProgress = parsed.prompt_progress;
+					if (abortSignal?.aborted) break;
 
-							const chunkModel = ChatService.extractModelName(parsed);
-							if (chunkModel && !modelEmitted) {
-								modelEmitted = true;
-								onModel?.(chunkModel);
-							}
-
-							if (parsed.id && !idEmitted) {
-								idEmitted = true;
-								onCompletionId?.(parsed.id);
-							}
-
-							if (promptProgress) {
-								ChatService.notifyTimings(undefined, promptProgress, onTimings);
-							}
-
-							if (timings) {
-								ChatService.notifyTimings(timings, promptProgress, onTimings);
-								lastTimings = timings;
-							}
-
-							if (content) {
-								finalizeOpenToolCallBatch();
-								aggregatedContent += content;
-								if (!abortSignal?.aborted) {
-									onChunk?.(content);
-								}
-							}
-
-							if (reasoningContent) {
-								finalizeOpenToolCallBatch();
-								fullReasoningContent += reasoningContent;
-								if (!abortSignal?.aborted) {
-									onReasoningChunk?.(reasoningContent);
-								}
-							}
-
-							processToolCallDelta(toolCalls);
-						} catch (e) {
-							console.error('Error parsing JSON chunk:', e);
+					if (value && value.byteLength > 0) {
+						segmentBytesRead += value.byteLength;
+						lastByteAt = Date.now();
+						if (!madeProgress) {
+							madeProgress = true;
+							onConnectionState?.(StreamConnectionState.STREAMING);
 						}
 					}
+
+					chunk += decoder.decode(value, { stream: true });
+					const lines = chunk.split(SSE_LINE_SEPARATOR);
+					chunk = lines.pop() || '';
+
+					// the persisted offset must point right after the last fully parsed line,
+					// the trailing `chunk` is partial bytes still waiting for a newline
+					if (conversationId) {
+						const tailBytes = encoder.encode(chunk).byteLength;
+						bytesParsed = segmentStartOffset + segmentBytesRead - tailBytes;
+						ChatService.saveStreamState(conversationId, bytesParsed, streamModel);
+					}
+
+					for (const line of lines) {
+						if (abortSignal?.aborted) break;
+
+						if (line.startsWith(SSE_DATA_PREFIX)) {
+							const data = line.slice(SSE_DATA_PREFIX.length).trim();
+							if (data === SSE_DONE_MARKER) {
+								streamFinished = true;
+
+								continue;
+							}
+
+							try {
+								const parsed: ApiChatCompletionStreamChunk = JSON.parse(data);
+								const choice = parsed.choices?.[0];
+								const content = choice?.delta?.content;
+								const reasoningContent = choice?.delta?.reasoning_content;
+								const toolCalls = choice?.delta?.tool_calls;
+								const timings = parsed.timings;
+								const promptProgress = parsed.prompt_progress;
+
+								const chunkModel = ChatService.extractModelName(parsed);
+								if (chunkModel && !modelEmitted) {
+									modelEmitted = true;
+									onModel?.(chunkModel);
+								}
+
+								if (parsed.id && !idEmitted) {
+									idEmitted = true;
+									onCompletionId?.(parsed.id);
+								}
+
+								if (promptProgress) {
+									ChatService.notifyTimings(undefined, promptProgress, onTimings);
+								}
+
+								if (timings) {
+									ChatService.notifyTimings(timings, promptProgress, onTimings);
+									lastTimings = timings;
+								}
+
+								if (content) {
+									finalizeOpenToolCallBatch();
+									aggregatedContent += content;
+									if (!abortSignal?.aborted) {
+										onChunk?.(content);
+									}
+								}
+
+								if (reasoningContent) {
+									finalizeOpenToolCallBatch();
+									fullReasoningContent += reasoningContent;
+									if (!abortSignal?.aborted) {
+										onReasoningChunk?.(reasoningContent);
+									}
+								}
+
+								processToolCallDelta(toolCalls);
+							} catch (e) {
+								console.error('Error parsing JSON chunk:', e);
+							}
+						}
+					}
+
+					if (abortSignal?.aborted) break;
+					if (streamFinished) break;
 				}
 
+				// inner reader done, decide whether to try a resume
 				if (abortSignal?.aborted) break;
+				if (streamFinished) break;
+				if (!conversationId) break;
+
+				if (!madeProgress) {
+					onConnectionState?.(StreamConnectionState.LOST);
+					onError?.(new Error('Stream resume produced no new bytes, giving up'));
+					break;
+				}
+
+				onConnectionState?.(StreamConnectionState.RESUMING);
+				madeProgress = false;
+
+				// the server resends starting at bytesParsed, discard any partial line we held, it
+				// will be retransmitted from a clean line boundary. reuse the frozen model, not the
+				// live dropdown
+				const resumeResp = await ChatService.resumeStream(
+					conversationId,
+					abortSignal,
+					streamModel
+				).catch(() => null);
+				// an abort landing during the resume request is intentional, not a lost connection
+				if (abortSignal?.aborted) break;
+				if (!resumeResp || resumeResp.status !== 200) {
+					onConnectionState?.(StreamConnectionState.LOST);
+					onError?.(new Error('Stream connection lost and could not be resumed'));
+					break;
+				}
+				const newReader = resumeResp.body?.getReader();
+				if (!newReader) break;
+
+				try {
+					reader.releaseLock();
+				} catch {
+					/* ignore */
+				}
+				reader = newReader;
+				decoder = new TextDecoder();
+				chunk = '';
+				segmentStartOffset = bytesParsed;
+				segmentBytesRead = 0;
+				lastByteAt = Date.now();
 			}
 
 			if (abortSignal?.aborted) return;
@@ -718,6 +972,10 @@ export class ChatService {
 			if (streamFinished) {
 				finalizeOpenToolCallBatch();
 
+				if (conversationId) {
+					ChatService.clearStreamState(conversationId);
+				}
+
 				const finalToolCalls =
 					aggregatedToolCalls.length > 0 ? JSON.stringify(aggregatedToolCalls) : undefined;
 
@@ -735,7 +993,14 @@ export class ChatService {
 
 			throw err;
 		} finally {
-			reader.releaseLock();
+			if (typeof document !== 'undefined') {
+				document.removeEventListener('visibilitychange', onVisibilityChange);
+			}
+			try {
+				reader.releaseLock();
+			} catch {
+				/* ignore */
+			}
 		}
 	}
 

tools/ui/src/lib/services/mcp.service.ts

@@ -628,19 +628,20 @@ export class MCPService {
 		);
 
 		const runtimeErrorHandler = (error: Error) => {
-			// Ignore errors that are expected when the SDK's transport is closed,
-			// or when connecting to servers that don't support SSE (stateless-only
-			// endpoints returning 405). The SDK wraps the original AbortError in
-			// a new Error with the message "SSE stream disconnected: AbortError",
-			// and also produces "Cannot cancel a stream locked by a reader".
-			// DOMException is thrown by the browser when aborting fetch requests.
-			const msg = error.message || String(error);
+			// the SDK reports any post initialize error here, including the abort we trigger
+			// ourselves on the next health check cycle, on tab unload, or on server teardown.
+			// these are lifecycle aborts, not actionable errors, so we keep them out of the red console.
+			// the SDK wraps the original AbortError in a generic Error like
+			//   "SSE stream disconnected: AbortError: The operation was aborted."
+			// which isAbortError cannot recognize by name alone, so we also pattern match on the message
+			if (isAbortError(error)) {
+				return;
+			}
+			const msg = error?.message ?? '';
 			if (
-				error.name === 'AbortError' ||
-				error instanceof DOMException ||
-				msg.includes('SSE stream disconnected') ||
-				msg.includes('stream locked by a reader') ||
-				msg.includes('The operation was aborted')
+				/SSE stream disconnected:.*AbortError/i.test(msg) ||
+				/AbortError: .*aborted/i.test(msg) ||
+				/stream locked by a reader/i.test(msg)
 			) {
 				return;
 			}

tools/ui/src/lib/stores/agentic.svelte.ts

@@ -614,7 +614,7 @@ class AgenticStore {
 							throw error;
 						}
 					},
-					undefined,
+					conversationId,
 					signal
 				);
 

tools/ui/src/lib/stores/chat.svelte.ts

@@ -11,9 +11,11 @@
  * @see ChatService in services/chat.service.ts for API operations
  */
 
-import { SvelteMap } from 'svelte/reactivity';
+import { SvelteMap, SvelteSet } from 'svelte/reactivity';
 import { DatabaseService } from '$lib/services/database.service';
 import { ChatService } from '$lib/services/chat.service';
+import { streamIdentity } from '$lib/utils/stream-identity';
+import { getAuthHeaders } from '$lib/utils/api-headers';
 import { conversationsStore } from '$lib/stores/conversations.svelte';
 import { config } from '$lib/stores/settings.svelte';
 import { agenticStore } from '$lib/stores/agentic.svelte';
@@ -49,10 +51,17 @@ import type {
 import type {
 	ApiChatMessageData,
 	ApiProcessingState,
+	ApiStreamSession,
 	DatabaseMessage,
 	DatabaseMessageExtra
 } from '$lib/types';
-import { ContinueIntentKind, ErrorDialogType, MessageRole, MessageType } from '$lib/enums';
+import {
+	ContinueIntentKind,
+	ErrorDialogType,
+	MessageRole,
+	MessageType,
+	StreamConnectionState
+} from '$lib/enums';
 
 interface ConversationStateEntry {
 	lastAccessed: number;
@@ -65,9 +74,25 @@ class ChatStore {
 	isLoading = $state(false);
 	// true while the active conversation streams reasoning content but no visible content yet
 	isReasoning = $state(false);
+	// resumable stream connection state for the active conversation
+	// streaming -> bytes flowing normally, resuming -> waiting on /v1/stream/:id reconnect, lost -> unrecoverable
+	streamConnectionState = $state<StreamConnectionState>(StreamConnectionState.STREAMING);
 	chatLoadingStates = new SvelteMap<string, boolean>();
 	chatReasoningStates = new SvelteMap<string, boolean>();
-	chatStreamingStates = new SvelteMap<string, { response: string; messageId: string }>();
+	chatStreamingStates = new SvelteMap<
+		string,
+		{ response: string; messageId: string; model?: string | null }
+	>();
+	// convs that the backend reports as having a running session, populated by the global sync
+	// at app mount and on visibilitychange. it does not overlap with chatLoadingStates which
+	// tracks inferences driven by this browser, both are unioned to feed the sidebar spinners
+	private remoteRunningConvs = new SvelteSet<string>();
+	// per conv attach lifecycle, used to derive the global streaming flag without flipping it
+	// off when one conv finishes while another is still streaming. mirrors chatLoadingStates
+	// in scope but tracks the attach + tee replay path specifically
+	private attachingConvs = new SvelteSet<string>();
+	// in-flight discoverActiveStream guard, keyed by conv id
+	private discoveringConvs = new SvelteSet<string>();
 	private abortControllers = new SvelteMap<string, AbortController>();
 	private preEncodeAbortController: AbortController | null = null;
 	private processingStates = new SvelteMap<string, ApiProcessingState | null>();
@@ -98,6 +123,11 @@ class ChatStore {
 			this.chatLoadingStates.delete(convId);
 			if (convId === conversationsStore.activeConversation?.id) this.isLoading = false;
 			this.setChatReasoning(convId, false);
+			// the local pipe is the authoritative observer of session end: when it finishes (clean
+			// onComplete or explicit Stop), the backend session is finalized too, so we drop the
+			// sidebar hint for this conv right away instead of waiting for the next visibilitychange
+			// snapshot. without this the spinner ghosts until the user toggles the tab
+			this.remoteRunningConvs.delete(convId);
 		}
 	}
 
@@ -110,9 +140,18 @@ class ChatStore {
 			if (convId === conversationsStore.activeConversation?.id) this.isReasoning = false;
 		}
 	}
-	private setChatStreaming(convId: string, response: string, messageId: string): void {
+	private setChatStreaming(
+		convId: string,
+		response: string,
+		messageId: string,
+		model?: string | null
+	): void {
 		this.touchConversationState(convId);
-		this.chatStreamingStates.set(convId, { response, messageId });
+		this.chatStreamingStates.set(convId, {
+			response,
+			messageId,
+			model: model ?? this.chatStreamingStates.get(convId)?.model
+		});
 		if (convId === conversationsStore.activeConversation?.id) this.currentResponse = response;
 	}
 	private clearChatStreaming(convId: string): void {
@@ -137,6 +176,314 @@ class ChatStore {
 			}
 		}
 	}
+	/**
+	 * Server side stream discovery, split in three pieces:
+	 *
+	 * probeServerStream(convId) -> hits POST /v1/streams/lookup with the conv id, returns the session to attach
+	 *   to or null. Pure read, no side effect, no UI lock. Safe to fire in parallel with anything.
+	 *
+	 * attachServerStream(convId) -> flips the spinner immediately, fetches the replay stream
+	 *   from byte 0, finds the assistant slot to splice into (creates a placeholder if the conv has
+	 *   no assistant message yet, for cross device or fresh local DB cases), and pipes the SSE bytes
+	 *   into the message via handleStreamResponse.
+	 *
+	 * discoverActiveStream(convId) -> probe + attach in one call. Used by callers that do not need
+	 *   to overlap the probe with other async work.
+	 *
+	 * The mount of the chat page in +page.svelte calls probeServerStream in parallel with
+	 * loadConversation, then attachServerStream once both have settled. This gives the earliest
+	 * possible time to spinner and avoids racing against an empty activeMessages array.
+	 */
+	async probeServerStream(convId: string): Promise<ApiStreamSession | null> {
+		if (!convId) return null;
+		let listResp: Response;
+		try {
+			// POST the one conv id we are probing
+			listResp = await fetch(`./v1/streams/lookup`, {
+				method: 'POST',
+				headers: { ...getAuthHeaders(), 'Content-Type': 'application/json' },
+				body: JSON.stringify({ conversation_ids: [convId] })
+			});
+		} catch (e) {
+			console.warn('probeServerStream fetch failed:', e);
+			return null;
+		}
+		if (!listResp.ok) {
+			console.warn(`probeServerStream got HTTP ${listResp.status} for conv ${convId}`);
+			return null;
+		}
+		let sessions: ApiStreamSession[];
+		try {
+			sessions = (await listResp.json()) as ApiStreamSession[];
+		} catch (e) {
+			console.warn('probeServerStream JSON parse failed:', e);
+			return null;
+		}
+		return ChatService.selectActiveStream(sessions);
+	}
+
+	async attachServerStream(convId: string, streamId?: string): Promise<void> {
+		if (!convId) return;
+		if (this.chatStreamingStates.has(convId)) return;
+
+		// flip the spinner immediately, the user sees activity as soon as the conv becomes active.
+		// the global isStreamingActive flag is derived from attachingConvs.size, so adding here
+		// turns it on, and removing in unlock only turns it off when this is the last attach
+		this.setChatLoading(convId, true);
+		this.attachingConvs.add(convId);
+		this.setStreamingActive(true);
+		// only set the active processing conv if we are looking at it, otherwise a background
+		// attach would steal the indicator from the conv the user is currently viewing
+		if (convId === conversationsStore.activeConversation?.id) {
+			this.setActiveProcessingConversation(convId);
+		}
+
+		const unlock = () => {
+			this.attachingConvs.delete(convId);
+			// flip the global flag off only when no other conv is still attaching
+			if (this.attachingConvs.size === 0) {
+				this.setStreamingActive(false);
+			}
+			this.setChatLoading(convId, false);
+			this.clearChatStreaming(convId);
+		};
+
+		// fetch the replay stream from byte 0, rebuild the assistant message from scratch.
+		// resolve the server side identity, fall back to streamIdentity when the caller does not
+		// pass a streamId. probeServerStream returns the full id (with ::model suffix when present)
+		const id = streamId || streamIdentity(convId, selectedModelName());
+		let response: Response;
+		try {
+			response = await fetch(`./v1/stream/${encodeURIComponent(id)}?from=0`, {
+				headers: getAuthHeaders()
+			});
+		} catch (e) {
+			console.error('attachServerStream replay fetch failed:', e);
+			unlock();
+			return;
+		}
+		if (!response.ok) {
+			console.warn(`attachServerStream replay got HTTP ${response.status} for conv ${convId}`);
+			unlock();
+			return;
+		}
+
+		// load the target conversation messages by id, not via the active store. when multiple
+		// attaches run in parallel the active store may reflect another conv and writing through
+		// its index mixes content across convs (CoT flicker, message bleed). by going through the
+		// DB we stay isolated, and only mirror into the active store when the attached conv is
+		// the one currently displayed
+		let messages: DatabaseMessage[];
+		try {
+			messages = await DatabaseService.getConversationMessages(convId);
+		} catch (e) {
+			console.error('attachServerStream load messages failed:', e);
+			unlock();
+			return;
+		}
+
+		// locate the slot to splice into, create a placeholder assistant message if there is none.
+		// we use the conv-scoped findLastAssistantIdx helpers, they only depend on the array
+		let targetIdx = this.findLastAssistantIdx(messages);
+		if (targetIdx === -1) {
+			const lastUserIdx = this.findLastUserIdx(messages);
+			if (lastUserIdx === -1) {
+				console.warn(
+					`attachServerStream: conv ${convId} has no user or assistant message, cannot splice`
+				);
+				unlock();
+				return;
+			}
+			try {
+				const placeholder = await DatabaseService.createMessageBranch(
+					{
+						convId,
+						role: MessageRole.ASSISTANT,
+						content: '',
+						type: MessageType.TEXT,
+						timestamp: Date.now(),
+						parent: messages[lastUserIdx].id,
+						children: [],
+						toolCalls: ''
+					} as Omit<DatabaseMessage, 'id'>,
+					messages[lastUserIdx].id
+				);
+				messages = [...messages, placeholder];
+				targetIdx = messages.length - 1;
+				// only push into the active store when this conv is the one displayed right now
+				if (convId === conversationsStore.activeConversation?.id) {
+					conversationsStore.addMessageToActive(placeholder);
+				}
+			} catch (e) {
+				console.error('attachServerStream placeholder creation failed:', e);
+				unlock();
+				return;
+			}
+		}
+		if (targetIdx === -1) {
+			unlock();
+			return;
+		}
+		const targetMessage = messages[targetIdx];
+		const targetMessageId = targetMessage.id;
+		// when the assistant slot already has content, the running session is a continue or
+		// another append flow and its buffer holds only the appended deltas. preserve the prefix
+		// and let the replay add to it. when the slot is empty the session buffer holds the whole
+		// message so we wipe and rebuild from byte 0
+		const existingContent = targetMessage.content ?? '';
+		const existingReasoning = targetMessage.reasoningContent ?? '';
+		const isAppendMode = existingContent.length > 0;
+
+		// helper: write to the active store only when the attached conv is currently displayed.
+		// the lookup by message id is robust to reordering of activeMessages, two parallel attaches
+		// can no longer step on each other's indices
+		const writeActive = (updates: Partial<DatabaseMessage>) => {
+			if (convId !== conversationsStore.activeConversation?.id) {
+				return;
+			}
+			const liveIdx = conversationsStore.findMessageIndex(targetMessageId);
+			if (liveIdx === -1) return;
+			conversationsStore.updateMessageAtIndex(liveIdx, updates);
+		};
+
+		if (!isAppendMode) {
+			writeActive({ content: '', reasoningContent: undefined });
+		}
+
+		// extract the model suffix, the resume calls in handleStreamResponse must reuse the model
+		// the session was tagged with, not the live dropdown
+		const sepIdx = id.indexOf('::');
+		const attachedModel: string | null = sepIdx === -1 ? null : id.slice(sepIdx + 2);
+		this.setChatStreaming(convId, existingContent, targetMessageId, attachedModel);
+		const abortController = this.getOrCreateAbortController(convId);
+
+		let streamedContent = '';
+		let streamedReasoningContent = '';
+
+		const cleanup = () => {
+			unlock();
+			this.setProcessingState(convId, null);
+		};
+
+		try {
+			await ChatService.handleStreamResponse(
+				response,
+				(chunk: string) => {
+					streamedContent += chunk;
+					const displayed = isAppendMode ? existingContent + streamedContent : streamedContent;
+					writeActive({ content: displayed });
+					this.setChatStreaming(convId, displayed, targetMessageId);
+				},
+				async (
+					finalContent?: string,
+					reasoningContent?: string,
+					timings?: ChatMessageTimings,
+					toolCalls?: string
+				) => {
+					const streamed = streamedContent || finalContent || '';
+					const streamedR = streamedReasoningContent || reasoningContent || '';
+					const content = isAppendMode ? existingContent + streamed : streamed;
+					const reasoning = isAppendMode ? existingReasoning + streamedR : streamedR;
+					// the DB write is the source of truth, mirror to the active store only when
+					// the conv is currently displayed
+					await DatabaseService.updateMessage(targetMessageId, {
+						content,
+						reasoningContent: reasoning || undefined,
+						toolCalls: toolCalls || '',
+						timings
+					});
+					writeActive({
+						content,
+						reasoningContent: reasoning || undefined,
+						timings
+					});
+					cleanup();
+				},
+				(err: Error) => {
+					console.error('attachServerStream pipe error:', err);
+					cleanup();
+				},
+				(chunk: string) => {
+					streamedReasoningContent += chunk;
+					const displayed = isAppendMode
+						? existingReasoning + streamedReasoningContent
+						: streamedReasoningContent;
+					writeActive({ reasoningContent: displayed });
+				},
+				undefined,
+				undefined,
+				undefined,
+				undefined,
+				convId,
+				abortController.signal,
+				(connState: StreamConnectionState) => {
+					if (convId === conversationsStore.activeConversation?.id) {
+						this.streamConnectionState = connState;
+					}
+				},
+				attachedModel
+			);
+		} catch (e) {
+			console.error('attachServerStream pipe crashed:', e);
+			cleanup();
+		}
+	}
+
+	async discoverActiveStream(convId: string): Promise<void> {
+		if (!convId) return;
+		if (this.chatStreamingStates.has(convId)) return;
+		if (this.chatLoadingStates.get(convId)) return;
+		// concurrency guard: another discover may already be running for this conv (typical race
+		// between mount and visibilitychange on tab switch). a second concurrent fetch on the same
+		// /v1/stream/<id> would duplicate every byte into the DB message, this guard bounces it
+		if (this.discoveringConvs.has(convId)) return;
+		this.discoveringConvs.add(convId);
+
+		try {
+			// the model is frozen at POST time, rebuild the exact conv::model identity from the
+			// persisted state so the lookup key matches what the server stored. null means a single
+			// model conv with no ::suffix, only guess from the dropdown with no persisted state
+			const localState = ChatService.getStreamState(convId);
+			const streamId = ChatService.resumeStreamIdentity(convId, localState, selectedModelName());
+
+			// primary path: ask the server which sessions exist for this identity
+			const serverTarget = await this.probeServerStream(streamId);
+			if (serverTarget) {
+				// pass the full server side identity (may carry a ::model suffix) so the GET routes
+				// straight to the owning session, no probe or fan out
+				await this.attachServerStream(convId, serverTarget.conversation_id);
+				return;
+			}
+
+			// fallback: local state remembers an interrupted byte offset for this conv, the server may
+			// still have a live session matching that identity (we just lost the bytes mid stream). retry
+			// with the frozen identity, the server probe inside attachServerStream tells us if it exists
+			if (!localState) {
+				return;
+			}
+			await this.attachServerStream(convId, streamId);
+			// if attachServerStream failed (session gone, TTL expired), clear the local state to avoid retrying forever
+			if (!this.chatStreamingStates.has(convId) && !this.chatLoadingStates.get(convId)) {
+				ChatService.clearStreamState(convId);
+			}
+		} finally {
+			this.discoveringConvs.delete(convId);
+		}
+	}
+
+	private findLastAssistantIdx(messages: DatabaseMessage[]): number {
+		for (let i = messages.length - 1; i >= 0; i--) {
+			if (messages[i].role === MessageRole.ASSISTANT) return i;
+		}
+		return -1;
+	}
+
+	private findLastUserIdx(messages: DatabaseMessage[]): number {
+		for (let i = messages.length - 1; i >= 0; i--) {
+			if (messages[i].role === MessageRole.USER) return i;
+		}
+		return -1;
+	}
 
 	clearUIState(): void {
 		this.isLoading = false;
@@ -265,13 +612,83 @@ class ChatStore {
 	}
 
 	getAllLoadingChats(): string[] {
-		return Array.from(this.chatLoadingStates.keys());
+		// union of local (this browser is piping) and remote (backend reports a running session
+		// for this conv but no local pipe yet) sources. the sidebar shows one spinner per entry
+		const out = new SvelteSet<string>(this.chatLoadingStates.keys());
+		for (const id of this.remoteRunningConvs) {
+			out.add(id);
+		}
+		return Array.from(out);
 	}
 
 	getAllStreamingChats(): string[] {
 		return Array.from(this.chatStreamingStates.keys());
 	}
 
+	/**
+	 * Resync the remote running convs set from the backend. Called by the layout at mount and on
+	 * visibilitychange, no polling. A snapshot semantic: the set is replaced wholesale, stale entries
+	 * for sessions that finalized while the browser was elsewhere are dropped naturally.
+	 */
+	async syncRemoteRunningStreams(): Promise<void> {
+		// the conversations store loads from IndexedDB asynchronously, the +layout onMount caller
+		// fires before that finishes. read ids straight from the DB so the result does not depend
+		// on the store init race, and the sidebar spinners light up at first paint for every conv
+		// the user owns even if it has not been hydrated into the store yet
+		let ids: string[];
+		try {
+			const all = await DatabaseService.getAllConversations();
+			ids = all.map((c) => c.id).filter((id) => !!id);
+		} catch (e) {
+			console.warn('syncRemoteRunningStreams DB read failed:', e);
+			return;
+		}
+		// only ask about conv ids the user already owns
+		if (ids.length === 0) {
+			for (const id of Array.from(this.remoteRunningConvs)) {
+				this.remoteRunningConvs.delete(id);
+			}
+			return;
+		}
+		// rebuild the frozen conv::model identity per conv so a session started with a model still
+		// matches. the server response is mapped back to the bare id below for the sidebar set
+		const lookupIds = ids.map((id) =>
+			ChatService.resumeStreamIdentity(id, ChatService.getStreamState(id), null)
+		);
+		let sessions: ApiStreamSession[];
+		try {
+			const resp = await fetch('./v1/streams/lookup', {
+				method: 'POST',
+				headers: { ...getAuthHeaders(), 'Content-Type': 'application/json' },
+				body: JSON.stringify({ conversation_ids: lookupIds })
+			});
+			if (!resp.ok) return;
+			const body = (await resp.json()) as unknown;
+			if (!Array.isArray(body)) return;
+			sessions = body as ApiStreamSession[];
+		} catch (e) {
+			console.warn('syncRemoteRunningStreams fetch failed:', e);
+			return;
+		}
+		const running = new SvelteSet<string>();
+		for (const s of sessions) {
+			if (s && !s.is_done && typeof s.conversation_id === 'string' && s.conversation_id) {
+				// strip the optional ::model suffix, the sidebar set is keyed by the bare conv id
+				const sepIdx = s.conversation_id.indexOf('::');
+				const bareId = sepIdx === -1 ? s.conversation_id : s.conversation_id.slice(0, sepIdx);
+				running.add(bareId);
+			}
+		}
+		for (const id of Array.from(this.remoteRunningConvs)) {
+			if (!running.has(id)) {
+				this.remoteRunningConvs.delete(id);
+			}
+		}
+		for (const id of running) {
+			this.remoteRunningConvs.add(id);
+		}
+	}
+
 	getChatStreamingPublic(convId: string): { response: string; messageId: string } | undefined {
 		return this.getChatStreaming(convId);
 	}
@@ -922,6 +1339,11 @@ class ChatStore {
 				onModel: streamCallbacks.onModel,
 				onCompletionId: streamCallbacks.onCompletionId,
 				onTimings: streamCallbacks.onTimings,
+				onConnectionState: (state: StreamConnectionState) => {
+					if (convId === conversationsStore.activeConversation?.id) {
+						this.streamConnectionState = state;
+					}
+				},
 				onComplete: async (
 					finalContent?: string,
 					reasoningContent?: string,
@@ -979,6 +1401,12 @@ class ChatStore {
 	async stopGenerationForChat(convId: string): Promise<void> {
 		await this.savePartialResponseIfNeeded(convId);
 		this.setStreamingActive(false);
+		// tell the server to stop the generation, not just drop the HTTP socket. without this the
+		// detached drain keeps producing tokens until eos or max_tokens. use the frozen identity
+		// captured when the session started, not the live dropdown
+		const streamStateForStop = this.chatStreamingStates.get(convId);
+		const modelForStop = streamStateForStop?.model ?? selectedModelName();
+		void ChatService.cancelServerStream(convId, modelForStop);
 		this.abortRequest(convId);
 		this.setChatLoading(convId, false);
 		this.clearChatStreaming(convId);
@@ -1393,7 +1821,11 @@ class ChatStore {
 
 			const updateStreamingContent = (fullContent: string) => {
 				this.setChatStreaming(msg.convId, fullContent, msg.id);
-				conversationsStore.updateMessageAtIndex(idx, { content: fullContent });
+				// resolve the row by id on every write, switching to another conv mid continue makes
+				// this a no op instead of writing positionally into the now displayed conversation
+				conversationsStore.updateMessageAtIndex(conversationsStore.findMessageIndex(msg.id), {
+					content: fullContent
+				});
 			};
 
 			const abortController = this.getOrCreateAbortController(msg.convId);
@@ -1403,6 +1835,11 @@ class ChatStore {
 				{
 					...this.getApiOptions(),
 					continueFinalMessage: true,
+					onConnectionState: (state: StreamConnectionState) => {
+						if (msg.convId === conversationsStore.activeConversation?.id) {
+							this.streamConnectionState = state;
+						}
+					},
 					onChunk: (chunk: string) => {
 						appendedContent += chunk;
 						hasReceivedContent = true;
@@ -1414,7 +1851,7 @@ class ChatStore {
 						hasReceivedContent = true;
 						// mark streaming state so a stop mid-thinking can persist the partial reasoning
 						this.setChatStreaming(msg.convId, originalContent + appendedContent, msg.id);
-						conversationsStore.updateMessageAtIndex(idx, {
+						conversationsStore.updateMessageAtIndex(conversationsStore.findMessageIndex(msg.id), {
 							reasoningContent: originalReasoning + appendedReasoning
 						});
 						this.setChatReasoning(msg.convId, true);
@@ -1455,7 +1892,7 @@ class ChatStore {
 							timings
 						});
 
-						conversationsStore.updateMessageAtIndex(idx, {
+						conversationsStore.updateMessageAtIndex(conversationsStore.findMessageIndex(msg.id), {
 							content: fullContent,
 							reasoningContent: fullReasoning,
 							timestamp: Date.now(),
@@ -1477,11 +1914,14 @@ class ChatStore {
 									timestamp: Date.now()
 								});
 
-								conversationsStore.updateMessageAtIndex(idx, {
-									content: originalContent + appendedContent,
-									reasoningContent: originalReasoning + appendedReasoning || undefined,
-									timestamp: Date.now()
-								});
+								conversationsStore.updateMessageAtIndex(
+									conversationsStore.findMessageIndex(msg.id),
+									{
+										content: originalContent + appendedContent,
+										reasoningContent: originalReasoning + appendedReasoning || undefined,
+										timestamp: Date.now()
+									}
+								);
 							}
 
 							this.setChatLoading(msg.convId, false);
@@ -1498,7 +1938,7 @@ class ChatStore {
 							reasoningContent: originalReasoning + appendedReasoning || undefined,
 							timestamp: Date.now()
 						});
-						conversationsStore.updateMessageAtIndex(idx, {
+						conversationsStore.updateMessageAtIndex(conversationsStore.findMessageIndex(msg.id), {
 							content: originalContent + appendedContent,
 							reasoningContent: originalReasoning + appendedReasoning || undefined,
 							timestamp: Date.now()

tools/ui/src/lib/types/api.d.ts

@@ -512,3 +512,18 @@ export interface ApiRouterModelsUnloadResponse {
 	success: boolean;
 	error?: string;
 }
+
+/**
+ * Entry returned by POST /v1/streams/lookup. The client passes the conv ids it owns in the body
+ * and the server returns one entry per matching live or recently completed background streaming
+ * session, keyed by conversation_id. The WebUI uses this at mount and on visibilitychange to
+ * populate sidebar spinners and to reattach to an ongoing inference for the active conversation.
+ * The server never lists ids the client did not ask about, so foreign random UUIDs stay private.
+ */
+export interface ApiStreamSession {
+	conversation_id: string;
+	is_done: boolean;
+	total_bytes: number;
+	started_at: number;
+	completed_at: number;
+}

tools/ui/src/lib/types/index.ts

@@ -34,7 +34,8 @@ export type {
 	ApiRouterModelsListResponse,
 	ApiRouterModelsUnloadRequest,
 	ApiRouterModelsUnloadResponse,
-	AudioInputFormat
+	AudioInputFormat,
+	ApiStreamSession
 } from './api';
 
 // Chat types

tools/ui/src/lib/types/settings.d.ts

@@ -4,9 +4,10 @@ import type { OpenAIToolDefinition } from './mcp';
 import type { DatabaseMessageExtra } from './database';
 import type {
 	ParameterSource,
-	ReasoningEffort,
 	SyncableParameterType,
-	SettingsFieldType
+	SettingsFieldType,
+	StreamConnectionState,
+	ReasoningEffort
 } from '$lib/enums';
 import type { Icon } from '@lucide/svelte';
 import type { Component } from 'svelte';
@@ -119,6 +120,7 @@ export interface SettingsChatServiceOptions {
 		toolCalls?: string
 	) => void;
 	onError?: (error: Error) => void;
+	onConnectionState?: (state: StreamConnectionState) => void;
 }
 
 export type SettingsConfigType = typeof SETTING_CONFIG_DEFAULT & {

tools/ui/src/lib/utils/abort.ts

@@ -6,6 +6,17 @@
  * when needed (e.g., user stops generation, navigates away, etc.).
  */
 
+// the standard DOMException name for a cancelled operation
+const ABORT_ERROR_NAME = 'AbortError';
+
+// browser specific TypeError messages emitted when a fetch reader is cut by page unload,
+// navigation, or a transient network drop. functionally aborts, not actionable errors
+const ABORT_LIKE_MESSAGE_PATTERNS = [
+	/input stream/i, // Firefox: stream cut at unload
+	/network connection was lost/i, // Safari: transient network drop
+	/load failed/i // Safari: page navigation during fetch
+];
+
 /**
  * Throws an AbortError if the signal is aborted.
  * Use this at the start of async operations to fail fast.
@@ -23,7 +34,7 @@
  */
 export function throwIfAborted(signal?: AbortSignal): void {
 	if (signal?.aborted) {
-		throw new DOMException('Operation was aborted', 'AbortError');
+		throw new DOMException('Operation was aborted', ABORT_ERROR_NAME);
 	}
 }
 
@@ -48,11 +59,18 @@ export function throwIfAborted(signal?: AbortSignal): void {
  * ```
  */
 export function isAbortError(error: unknown): boolean {
-	if (error instanceof DOMException && error.name === 'AbortError') {
+	if (error instanceof DOMException && error.name === ABORT_ERROR_NAME) {
 		return true;
 	}
-	if (error instanceof Error && error.name === 'AbortError') {
-		return true;
+	if (error instanceof Error) {
+		if (error.name === ABORT_ERROR_NAME) {
+			return true;
+		}
+		// these patterns are functionally aborts, keep them out of the red console
+		if (error instanceof TypeError) {
+			const msg = error.message ?? '';
+			if (ABORT_LIKE_MESSAGE_PATTERNS.some((re) => re.test(msg))) return true;
+		}
 	}
 	return false;
 }
@@ -133,7 +151,7 @@ export async function withAbortSignal<T>(promise: Promise<T>, signal?: AbortSign
 
 	return new Promise<T>((resolve, reject) => {
 		const abortHandler = () => {
-			reject(new DOMException('Operation was aborted', 'AbortError'));
+			reject(new DOMException('Operation was aborted', ABORT_ERROR_NAME));
 		};
 
 		signal.addEventListener('abort', abortHandler, { once: true });

tools/ui/src/lib/utils/stream-identity.ts

@@ -0,0 +1,13 @@
+/**
+ * Build the conversation identity used by the server side replay buffer.
+ *
+ * The server identifies a stream session by a conversation id sent in the
+ * X-Conversation-Id header. When the user has explicitly picked a model the
+ * client appends ::modelName, so a per model session stays distinct and the
+ * router resolves the owning child through its conv_id -> model map.
+ */
+export function streamIdentity(conversationId: string, model?: string | null): string {
+	if (!conversationId) return '';
+	if (!model) return conversationId;
+	return `${conversationId}::${model}`;
+}

tools/ui/src/routes/(chat)/chat/[id]/+page.svelte

@@ -4,7 +4,7 @@
 	import { afterNavigate } from '$app/navigation';
 	import { DialogModelNotAvailable } from '$lib/components/app';
 	import { APP_NAME, ROUTES } from '$lib/constants';
-	import { chatStore, isLoading } from '$lib/stores/chat.svelte';
+	import { chatStore } from '$lib/stores/chat.svelte';
 	import { conversationsStore, activeConversation } from '$lib/stores/conversations.svelte';
 	import { modelsStore, modelOptions } from '$lib/stores/models.svelte';
 
@@ -83,7 +83,7 @@
 
 			// Skip loading if this conversation is already active (e.g., just created)
 			if (activeConversation()?.id === chatId) {
-				// Still handle URL params even if conversation is active
+				void chatStore.discoverActiveStream(chatId);
 				if ((qParam !== null || modelParam !== null) && !urlParamsProcessed) {
 					handleUrlParams();
 				}
@@ -92,35 +92,33 @@
 
 			(async () => {
 				const success = await conversationsStore.loadConversation(chatId);
-				if (success) {
-					chatStore.syncLoadingStateForChat(chatId);
-
-					// Handle URL params after conversation is loaded
-					if ((qParam !== null || modelParam !== null) && !urlParamsProcessed) {
-						await handleUrlParams();
-					}
-				} else {
+				if (!success) {
 					await goto(ROUTES.START);
+					return;
+				}
+				chatStore.syncLoadingStateForChat(chatId);
+				// server probe (with localStorage fallback) and attach
+				await chatStore.discoverActiveStream(chatId);
+
+				if ((qParam !== null || modelParam !== null) && !urlParamsProcessed) {
+					await handleUrlParams();
 				}
 			})();
 		}
 	});
 
 	$effect(() => {
-		if (typeof window !== 'undefined') {
-			const handleBeforeUnload = () => {
-				if (isLoading()) {
-					console.log('Page unload detected while streaming - aborting stream');
-					chatStore.stopGeneration();
-				}
-			};
+		if (typeof window === 'undefined' || typeof document === 'undefined') return;
 
-			window.addEventListener('beforeunload', handleBeforeUnload);
-
-			return () => {
-				window.removeEventListener('beforeunload', handleBeforeUnload);
-			};
-		}
+		// when the tab comes back to the foreground, re-run discovery to catch any race
+		// where the initial mount probe missed an active session
+		const onVisibility = () => {
+			if (document.visibilityState !== 'visible') return;
+			if (!chatId) return;
+			void chatStore.discoverActiveStream(chatId);
+		};
+		document.addEventListener('visibilitychange', onVisibility);
+		return () => document.removeEventListener('visibilitychange', onVisibility);
 	});
 </script>
 

tools/ui/src/routes/+layout.svelte

@@ -11,6 +11,7 @@
 	import { PwaMetaTags, PwaRefreshAlert } from '$lib/components/pwa';
 	import { pwaAssetsHead } from 'virtual:pwa-assets/head';
 
+	import { chatStore } from '$lib/stores/chat.svelte';
 	import { conversationsStore } from '$lib/stores/conversations.svelte';
 	import * as Tooltip from '$lib/components/ui/tooltip';
 	import { isRouterMode, serverStore } from '$lib/stores/server.svelte';
@@ -154,8 +155,18 @@
 
 	onMount(() => {
 		updateFavicon();
+		// snapshot of every backend running stream on first load, populates the sidebar spinners
+		// so the user sees each conv that has a live inference, even ones not opened yet
+		void chatStore.syncRemoteRunningStreams();
 	});
 
+	// refresh that snapshot when the tab returns to the foreground, a stream may have advanced
+	// or ended while it was hidden. snapshot only, no polling
+	function handleVisibilityChange() {
+		if (document.visibilityState !== 'visible') return;
+		void chatStore.syncRemoteRunningStreams();
+	}
+
 	$effect(() => {
 		void theme.isSystemDark;
 
@@ -280,6 +291,7 @@
 </svelte:head>
 
 <svelte:window onkeydown={handleKeydown} bind:innerHeight bind:innerWidth />
+<svelte:document onvisibilitychange={handleVisibilityChange} />
 
 <Tooltip.Provider delayDuration={TOOLTIP_DELAY_DURATION}>
 	<div class="flex flex-col md:flex-row">

tools/ui/tests/unit/abort.test.ts

@@ -0,0 +1,56 @@
+import { describe, expect, it } from 'vitest';
+import { isAbortError } from '$lib/utils/abort';
+
+describe('isAbortError', () => {
+	it('returns false for null, undefined and non-error values', () => {
+		expect(isAbortError(null)).toBe(false);
+		expect(isAbortError(undefined)).toBe(false);
+		expect(isAbortError('string error')).toBe(false);
+		expect(isAbortError({ name: 'AbortError' })).toBe(false);
+		expect(isAbortError(42)).toBe(false);
+	});
+
+	it('returns true for DOMException with AbortError name', () => {
+		const err = new DOMException('Operation was aborted', 'AbortError');
+		expect(isAbortError(err)).toBe(true);
+	});
+
+	it('returns true for plain Error with AbortError name', () => {
+		const err = new Error('aborted');
+		err.name = 'AbortError';
+		expect(isAbortError(err)).toBe(true);
+	});
+
+	it('returns false for unrelated Error instances', () => {
+		expect(isAbortError(new Error('something failed'))).toBe(false);
+		expect(isAbortError(new TypeError('not related'))).toBe(false);
+		expect(isAbortError(new RangeError('out of range'))).toBe(false);
+	});
+
+	it('recognizes Firefox TypeError "Error in input stream" emitted at page unload', () => {
+		expect(isAbortError(new TypeError('Error in input stream'))).toBe(true);
+		expect(isAbortError(new TypeError('TypeError: Error in input stream'))).toBe(true);
+	});
+
+	it('recognizes Safari "The network connection was lost" during transient drop', () => {
+		expect(isAbortError(new TypeError('The network connection was lost.'))).toBe(true);
+	});
+
+	it('recognizes Safari "Load failed" during page navigation', () => {
+		expect(isAbortError(new TypeError('Load failed'))).toBe(true);
+	});
+
+	it('does NOT recognize generic TypeError messages as aborts', () => {
+		// matching too broadly would hide real bugs, the predicate must stay conservative
+		expect(isAbortError(new TypeError('Failed to fetch'))).toBe(false);
+		expect(isAbortError(new TypeError('Cannot read property of undefined'))).toBe(false);
+		expect(isAbortError(new TypeError('NetworkError when attempting to fetch resource'))).toBe(
+			false
+		);
+	});
+
+	it('is case insensitive on the matched substrings', () => {
+		expect(isAbortError(new TypeError('error in INPUT STREAM'))).toBe(true);
+		expect(isAbortError(new TypeError('the network connection WAS LOST'))).toBe(true);
+	});
+});

tools/ui/tests/unit/stream-discovery.test.ts

@@ -0,0 +1,74 @@
+import { describe, expect, it } from 'vitest';
+import { ChatService } from '$lib/services/chat.service';
+import type { ApiStreamSession } from '$lib/types';
+
+function makeSession(overrides: Partial<ApiStreamSession>): ApiStreamSession {
+	return {
+		conversation_id: 'conv',
+		is_done: true,
+		total_bytes: 0,
+		started_at: 0,
+		completed_at: 0,
+		...overrides
+	};
+}
+
+describe('selectActiveStream', () => {
+	it('returns null on empty input', () => {
+		expect(ChatService.selectActiveStream([])).toBeNull();
+	});
+
+	it('returns null on null or undefined input', () => {
+		expect(ChatService.selectActiveStream(null)).toBeNull();
+		expect(ChatService.selectActiveStream(undefined)).toBeNull();
+	});
+
+	it('returns the single session when it is running', () => {
+		const s = makeSession({ conversation_id: 'only', is_done: false, started_at: 42 });
+		expect(ChatService.selectActiveStream([s])).toBe(s);
+	});
+
+	it('returns null when the single session is finalized', () => {
+		const s = makeSession({ conversation_id: 'only', is_done: true, started_at: 42 });
+		expect(ChatService.selectActiveStream([s])).toBeNull();
+	});
+
+	it('prefers a still running session over a finalized one regardless of started_at', () => {
+		const finalized = makeSession({ conversation_id: 'old', is_done: true, started_at: 1000 });
+		const running = makeSession({ conversation_id: 'new', is_done: false, started_at: 10 });
+		expect(ChatService.selectActiveStream([finalized, running])?.conversation_id).toBe('new');
+		expect(ChatService.selectActiveStream([running, finalized])?.conversation_id).toBe('new');
+	});
+
+	it('among running sessions, picks the most recently started one', () => {
+		const a = makeSession({ conversation_id: 'a', is_done: false, started_at: 100 });
+		const b = makeSession({ conversation_id: 'b', is_done: false, started_at: 200 });
+		const c = makeSession({ conversation_id: 'c', is_done: false, started_at: 150 });
+		expect(ChatService.selectActiveStream([a, b, c])?.conversation_id).toBe('b');
+		expect(ChatService.selectActiveStream([c, a, b])?.conversation_id).toBe('b');
+	});
+
+	it('returns null when all sessions are finalized, the DB already holds the content', () => {
+		const a = makeSession({ conversation_id: 'a', is_done: true, started_at: 10 });
+		const b = makeSession({ conversation_id: 'b', is_done: true, started_at: 30 });
+		const c = makeSession({ conversation_id: 'c', is_done: true, started_at: 20 });
+		expect(ChatService.selectActiveStream([a, b, c])).toBeNull();
+	});
+
+	it('keeps the first match on ties when both are running with identical started_at', () => {
+		// reduce visits left to right, the initial accumulator stays unless a strictly greater value appears
+		const a = makeSession({ conversation_id: 'first', is_done: false, started_at: 50 });
+		const b = makeSession({ conversation_id: 'second', is_done: false, started_at: 50 });
+		expect(ChatService.selectActiveStream([a, b])?.conversation_id).toBe('first');
+	});
+
+	it('handles a typical realistic mix: two finalized old, one freshly running, one freshly finalized', () => {
+		const old1 = makeSession({ conversation_id: 'old1', is_done: true, started_at: 100 });
+		const old2 = makeSession({ conversation_id: 'old2', is_done: true, started_at: 200 });
+		const freshFin = makeSession({ conversation_id: 'freshFin', is_done: true, started_at: 500 });
+		const running = makeSession({ conversation_id: 'running', is_done: false, started_at: 400 });
+		expect(ChatService.selectActiveStream([old1, old2, freshFin, running])?.conversation_id).toBe(
+			'running'
+		);
+	});
+});

tools/ui/tests/unit/stream-resume.test.ts

@@ -0,0 +1,128 @@
+import { afterEach, beforeAll, beforeEach, describe, expect, it } from 'vitest';
+
+// node env unit project has no DOM, install a minimal localStorage backed by a Map
+beforeAll(() => {
+	const store = new Map<string, string>();
+	const polyfill: Storage = {
+		get length() {
+			return store.size;
+		},
+		clear: () => store.clear(),
+		getItem: (k) => (store.has(k) ? store.get(k)! : null),
+		key: (i) => Array.from(store.keys())[i] ?? null,
+		removeItem: (k) => {
+			store.delete(k);
+		},
+		setItem: (k, v) => {
+			store.set(k, String(v));
+		}
+	};
+	(globalThis as unknown as { localStorage: Storage }).localStorage = polyfill;
+});
+
+import { ChatService } from '$lib/services/chat.service';
+import { STREAM_RESUME_LOCALSTORAGE_KEY_PREFIX } from '$lib/constants';
+
+describe('ChatService stream resume', () => {
+	beforeEach(() => {
+		localStorage.clear();
+	});
+	afterEach(() => {
+		localStorage.clear();
+	});
+
+	it('returns null when no state exists for the conversation', () => {
+		expect(ChatService.getStreamState('conv-a')).toBeNull();
+	});
+
+	it('saves and reads back the byte count', () => {
+		ChatService.saveStreamState('conv-a', 4242);
+		const got = ChatService.getStreamState('conv-a');
+		expect(got).not.toBeNull();
+		expect(got!.bytesReceived).toBe(4242);
+		expect(typeof got!.updatedAt).toBe('number');
+	});
+
+	it('overwrites the previous byte count on a new save for the same conversation', () => {
+		ChatService.saveStreamState('conv-a', 100);
+		ChatService.saveStreamState('conv-a', 200);
+		const got = ChatService.getStreamState('conv-a');
+		expect(got!.bytesReceived).toBe(200);
+	});
+
+	it('keeps states for distinct conversations isolated', () => {
+		ChatService.saveStreamState('conv-a', 10);
+		ChatService.saveStreamState('conv-b', 20);
+		expect(ChatService.getStreamState('conv-a')!.bytesReceived).toBe(10);
+		expect(ChatService.getStreamState('conv-b')!.bytesReceived).toBe(20);
+	});
+
+	it('clears the state for a given conversation', () => {
+		ChatService.saveStreamState('conv-a', 10);
+		ChatService.clearStreamState('conv-a');
+		expect(ChatService.getStreamState('conv-a')).toBeNull();
+	});
+
+	it('ignores empty conversation id on save', () => {
+		ChatService.saveStreamState('', 1);
+		expect(ChatService.getStreamState('')).toBeNull();
+	});
+
+	it('returns null on corrupted storage payload', () => {
+		localStorage.setItem(`${STREAM_RESUME_LOCALSTORAGE_KEY_PREFIX}conv-a`, '{not-json');
+		expect(ChatService.getStreamState('conv-a')).toBeNull();
+	});
+
+	it('persists the model alongside the byte count', () => {
+		ChatService.saveStreamState('conv-a', 10, 'model-x');
+		expect(ChatService.getStreamState('conv-a')!.model).toBe('model-x');
+	});
+
+	it('stores a null model when none is provided', () => {
+		ChatService.saveStreamState('conv-a', 10);
+		expect(ChatService.getStreamState('conv-a')!.model).toBeNull();
+	});
+
+	it('overwrites the model on a new save for the same conversation', () => {
+		ChatService.saveStreamState('conv-a', 10, 'model-x');
+		ChatService.saveStreamState('conv-a', 20, 'model-y');
+		expect(ChatService.getStreamState('conv-a')!.model).toBe('model-y');
+	});
+
+	describe('resumeStreamIdentity', () => {
+		it('appends the persisted model so the resume key matches the frozen POST identity', () => {
+			ChatService.saveStreamState('conv-a', 10, 'model-x');
+			expect(
+				ChatService.resumeStreamIdentity('conv-a', ChatService.getStreamState('conv-a'), 'dropdown')
+			).toBe('conv-a::model-x');
+		});
+
+		it('keeps the bare conv id when the persisted model is null', () => {
+			ChatService.saveStreamState('conv-a', 10);
+			expect(
+				ChatService.resumeStreamIdentity('conv-a', ChatService.getStreamState('conv-a'), 'dropdown')
+			).toBe('conv-a');
+		});
+
+		it('falls back to the current model only when no state is persisted', () => {
+			expect(ChatService.resumeStreamIdentity('conv-a', null, 'dropdown')).toBe('conv-a::dropdown');
+		});
+
+		it('ignores the fallback when a state exists, the persisted value is authoritative', () => {
+			ChatService.saveStreamState('conv-a', 10, 'model-x');
+			expect(
+				ChatService.resumeStreamIdentity('conv-a', ChatService.getStreamState('conv-a'), 'dropdown')
+			).toBe('conv-a::model-x');
+		});
+
+		it('falls back when a legacy state has no model field', () => {
+			localStorage.setItem(
+				`${STREAM_RESUME_LOCALSTORAGE_KEY_PREFIX}conv-a`,
+				JSON.stringify({ bytesReceived: 10, updatedAt: 1 })
+			);
+			expect(
+				ChatService.resumeStreamIdentity('conv-a', ChatService.getStreamState('conv-a'), 'dropdown')
+			).toBe('conv-a::dropdown');
+		});
+	});
+});